外文翻译---液压密封完整性调查研究-液压系统(编辑修改稿)

外文翻译---液压密封完整性调查研究-液压系统(编辑修改稿)内容摘要：

edge of the score, five key points were selected and their coordinates were measured. The width and depth of the score were then measured. In addition, a circular arc fit to these five points was calculated. Thus, an approximate radius of the score could be obtained. Fig. 2. The 16score piston seals. Fig. 3. The profile of a score. 机电 工程学院 机械系机械设计制造及其自动化班 学生 毛祖庆 毕业设计 第 5页 共 13页 井冈山大学外文翻译用纸 4. Experimental results In the experiment, 100 sets of data were acquired at different internal leakage rates, with each set consisting of 40 records of AE signals measured at a certain leakage rate. Each record of AE signal contained 4096 points sampled at 5 MHz, from which AE parameters were calculated. For each AE parameter, results obtained from the 40 records were then averaged. In the following, all the results are the average values. For each record of AE signal, the AE count rate, denoted as _N AE, was calculated by dividing the AE counts by the signal duration. Both a fixed threshold and a floating threshold were used for counting. Since there was no welldefined procedure to choose the threshold value, a wide range of values were tried. For the fixed threshold, a value of yielded the best results, as shown in Fig. 4a. It is noted that the AE count rate drops fast as the internal leakage rate decreases. Fig. 4. AE count rate versus internal leakage rate For the floating threshold, the threshold value was set to be proportional to the rms value of the signal. The resulting AE count rate remained at a constant level, nom atter how the leakage rate varied. This is shown in Fig. 4b, where the AE count rate was obtained with the threshold equal to the rms value of the signal. It can be seen that there is no desirable trend in the AE count rate with respect to the leakage rate. 5. Predict the internal leakage rate As has been shown in the above, the energy content of AE signal is closely 机电 工程学院 机械系机械设计制造及其自动化班 学生 毛祖庆 毕业设计 第 6页 共 13页 井冈山大学外文翻译用纸 related to the internal leakage rate in the water hydraulic cylinder. Therefore, it may be used to predict the internal leakage rate. The error of prediction, then, is of interest. In the following, an empirical model is built to predict the internal leakage rate based on measured AE signals and the error of prediction is analysed with statistical methods. Due to the simplicity in calculation, the rms value Vrms is chosen instead of the energy Ef to characterise AE signals. From the previous experimental data, the relationship between the AE rms value Vrms and the internal leakage rate Qi is obtained using the least squares method, given by Qi=+. For a measured AE rms value, the internal leakage rate may be predicted with Eq. (7). Suppose the measured AE rms value is Vrms0. A 95% prediction interval for the true value of the internal leakage rate,denoted as Qi0, is given by where ^Qi is the internal leakage rate predicted by Eq. (7) based on the measured Vrms0 and d is a measure of the width of the prediction interval. Note that d is not a constant but varies with the measured AE rms value Vrms0. For the range of the internal leakage rates smaller than L/min, d is about L/min. Eq. (8) means that for the measured AE rms value Vrms0, the true value of the internal leakage rate Qi0 lies inside the intervale ^Qi d。 ^Qi t dT with 95% confidence. 6. Conclusions This paper analysed the characteristics of AE signals generated by internal leakage in a water hydraulic cylinder. Experiments were carefully designed, including the simulation of the internal leakage across the piston seals in a water。