Application Research Of Force Identification Based On Least Squares Method In The Frequency Domain

As the higher demand of ship noise especially cabin noise of IMO organization, the vibration control of machinery which is the primary excitation source on ships has been drawing more and more attention. The basic method solving the problem is to design machinery with low noise, and load identification is the premium condition for the design of low noise. Identifying the excitation characteristics of machineries accurately plays an important role in developing Green Shipping.Firstly, the developing history of dynamic load identification was reviewed. Traditional method and definition of excitation characterization of machinery were also introduced. On the base of modal theory, equations for load identification within time domain and frequency domain were both derived. The procedure of applying Least Square Methods in frequency domain was summarized.As to the difficulties of traditional method applied to engineering practice, a certain method constitute of "Modes Modification, Least Square Methods and Verification of Response Error" was proposed. And different forms of excitation were identified on an experiment system. Firstly, an accurate finite element modal was constructed based on test modes. And load was identified using Least Square Methods based on test responses. Comparing the result with directly-measured data, the identification results in single-frequency and multiple-frequency excitation situations were discussed respectively. At the same time the influence of the amount and position of the measuring points as well as the number of modes superposition on the accuracy of identification were analyzed.Because of the difficulties in measuring the inner excitation of machineries directly by sensors, it was introduced a method of calculating response error between calculating and test values to assess the accuracy of identification in this paper. The response error was then verified to be an effective parameter on the experimental system under a variety of situations including different number of mode and different composition of test points.Finaly, The characteristics of a centrifugal pump's inner excitation and transmission property were analyzed using the methods mentioned above and the control measures were proposed. Based on the measured vibration response of a centrifugal pump, the inner dynamic load of the pump was identified, according to the primary exciting frequency and amplitude obtained. And the specific frequency which was amplified by the support structure was filtered. With the identified load data, the primary vibrating source of the pump was analyzed. The structural optimization of the pump was made according to the identified load spectrum, and the response of modified structure was predicted. It was found that the predicted results coincided well with the measured results, with a 3dB discrepancy of the total vibration level. The results also show that vibration level of modified structure has reduced by 6.3 dB. It is confirmed the accuracy of the identified load spectrum and the feasibility for engineering practice through this procedure.