| The quantitative design of vibration and noise has become the core technical means to realize the green environmental protection design concept of high-end offshore equipment,and the platform structural vibration and structure-borne sound problems caused by the vibration excitation of power equipment have always been important research topics in related engineering fields.As a complex elastic system,the offshore platform has large length and width scale,dense modes,and extremely complex structural vibration propagation process.When the vibration energy of the equipment is transmitted to the main structure of the platform and the air medium of the platform through the base,it will be incident,transmitted and reflected at the connecting surface,and may be accompanied by energy conversion,which makes the vibration transmission and acoustic vibration law of the platform structure extremely complex,and there are basic problems such as coupling vibration of equipment and platform structure,multi-modal vibration of complex structure and coupled acoustic vibration of plate cavity that need to be further studied.Therefore,this paper takes the vibration energy transfer path as the main line,and studies the vibration characteristics of platform structure from the perspectives of excitation,transmission and response,explores the coupling vibration characteristics of power equipment and platform structure,reveals the complex multimodal vibration transfer law of platform structure,and explores the acoustic-vibration mechanism of platform cavity coupling system and the energy transfer mechanism in structural system.The design method of acoustic control of offshore platform structure is proposed and verified in practical engineering,aiming to provide a theoretical basis and methodological basis for the acoustic control of offshore platform structure.The main research work of this paper is as follows:Aiming at the vibration problem of coupling system between power equipment and platform structure,the vibration characteristics of the coupling system were studied by taking diesel generator sets as an example.Aiming at the problem that the number of platform meshes is large and the calculation and analysis time is too long,which is difficult to meet the requirements of engineering iterative design,based on the principle of dynamic similarity,a simplified method for the overall model of the coupling system of power equipment and platform structure that meets the dynamics of similar frequency intervals is proposed.The simplified model was used to analyze the modal characteristics,base impedance characteristics and vibration energy transfer law of the coupling system of diesel generator set and platform structure,and the influence of platform structure form and parameter changes on the vibration characteristics of the coupling system was explored.On this basis,a resonance avoidance design method for coupling system of power equipment and platform structure is proposed,and the effectiveness of the method is verified by example.Taking diesel generator sets as an example,the simplified method of coupling system model and the design method of resonance mode avoidance proposed are also applicable to other power equipment of the platform,laying a foundation for the coupling resonance avoidance design and vibration control method of power equipment and offshore platform structure.Aiming at the problem that the complex giant system of the offshore platform cannot quickly provide an effective structural vibration control scheme in the design or completion stage,the multi-modal vibration characteristics of the complex structure of the platform are studied based on the principle of structural dynamics with the platform structure vibration control as the goal.Firstly,the vibration characteristics of the overall structure of the platform are studied,and the transmission law of the vibration energy generated by the main power equipment in the platform structure is explored by combining numerical simulation and real ship testing,the multimodal vibration response of the platform structure is analyzed,and the correlation between the multi-modal vibration of the platform structure and the dynamic characteristics of the basic structural elements under the action of multi-frequency excitation load of the equipment is explored.Starting from the basic structural units,the vibration characteristics of typical structures of the platform such as beam system and plate frame are systematically discussed,the evolution mechanism of complex multimodal vibration of platform structure is revealed,and the influence of boundary conditions and structural parameters on the vibration characteristics of platform plate frame structure is explored.On this basis,from the perspective of structural vibration control,a modal avoidance design method of offshore platform plate frame structure is proposed,aiming to provide theoretical and technical support for the vibration control of offshore platform structure in the design stage.Based on the energy principle and improved Fourier series method,a theoretical model and solution method of acoustic vibration for typical plate-cavity coupling system of the platform are proposed.Based on the energy principle of structure-acoustic coupling system,the displacement function of elastic plate structure and the sound pressure function in the sound cavity were described by the improved Fourier series method,the unknown displacement coefficient and sound pressure function were solved by the Rayleigh-Ritz method,the effectiveness and accuracy of the method were verified by numerical examples,and the influence of system parameter changes on the acoustic vibration characteristics of the structure was explored.Based on this method,based on the statistical energy method,a high-precision analysis model of cabin noise of offshore platform is established,and the research on the transmission characteristics of platform structured sound is carried out,and the dominant component of excitation force of platform cabin noise is obtained.Research on cabin structural acoustic protection design based on main excitation sources was carried out,and the effects of sound absorption,vibration isolation and vibration damping on cabin structure-borne sound were discussed.The design method of structural acoustic quantitative control of offshore platform cabins is proposed,aiming to provide theoretical basis and applied research guidance for the structural acoustic control design of offshore platform.Finally,taking a new semi-submersible drilling platform as the research object,based on the proposed design method of resonance avoidance of coupling system of power equipment and platform structure,the design method of modal avoidance of platform plate structure and the design method of quantitative control of platform structure acoustics,the design of offshore platform structure low noise is carried out,and the effectiveness of this series of methods is verified by real ship tests. |
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