| Summary: | 碩士 === 國立臺灣海洋大學 === 系統工程暨造船學系 === 92 === Abstract
The helical spring possesses 6 degrees of freedom, thus when it is used as an isolator, it can absorb the vibration energy in 6 degrees of freedom. This article aims at discussing the spring constants of the helical spring at 6 degrees of freedom, as well as analyzing its vibration isolation properties. Meanwhile, the spring isolator will be applied to the I-frame of the shaft of a high-speed yacht to isolate the vibration. The isolation effectiveness is analyzed and compared with the experimental values to verify the correctness of the analysis model.
The vibration isolation principle of the spring isolator is related to its natural frequency. The natural frequency of the spring is , where k represents the spring constants of the 6 degrees of freedom respectively. When the ratio of vibration frequency of a body over natural frequency is larger than 4, a vibration isolation of over 90% can be achieved. While M is an effective mass supported by the spring isolator, which can be derived by utilizing the superposition principle of beam theory for case of shaft system. By using the computer software Ansys, the numerical simulation of the shaft’s vibration isolation is carried out, and the maximum error between the results of the analysis and the results of the land based experiment is approximately 10%~15%, which was mainly resulting from the assumed value of damping ratio and basically it was proved the feasibility of the computer analysis.
The result of I-frame’s vibration reduction experiment conducted on land shows that when the shaft is subjected to impulsive load, the vibration reduction of the vibration acceleration of the base-plate at the first 5 major peak vibration values is between 4.4~59.8dB. When the shaft is under horizontal or vertical excitation force, the first 5 major vibration values of the base-plate have attained a good vibration reduction in the range of 40%~99% in linear acceleration and angular acceleration.
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