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951.
传统的声强技术容易受到强大背景噪声的干扰,针对此问题本文提出一种新的噪声测试技术--选择性声强技术,并利用自行研制的噪声自动分析系统对其进行了研究,包括原理、算法及测试设备。研究结果表明:选择性声强技术可以将目标噪声源的辐射噪声从强大的背景噪声中分离出来,测量结果有效地反映了目标噪声源的声场分布状况,为目标噪声源的噪声辐射特性研究及噪声控制提供参考依据。 相似文献
952.
S. A. Gaikwad E. P. Samuel D. S. Patil D. K. Gautam 《Bulletin of Materials Science》2007,30(3):255-261
Temperature dependent analysis to achieve better performance by reducing threshold current requirements and field intensity
has been carried out for GaN/AlGaN heterostructure lasers. The mirror loss in the GaN cavity has been obtained as a function
of temperature and cavity length. The quantum efficiency has been deduced for different values of cavity length. Dependence
of recombination rate on band gap and temperature has been investigated. Threshold current density has been deduced for GaN
lasers and effect of temperature on it has been investigated. The near field intensity analysis has been carried out at different
temperatures for 10% aluminum mole fraction in GaN/AlGaN heterostructure lasers. Furthermore, the effective index and FWHM
of near field has been investigated as a function of temperature. It has been deduced from our analysis that temperature has
a dominant effect on the threshold conditions and near field intensity in the wide band gap GaN based lasers. 相似文献
953.
954.
955.
A metal matrix composite (MMC) was fabricated using Al as the base metal which was reinforced by a ceramic material silica gel. This article shows detail fabrication stages in the production of MMC. The properties were considered with regard to the saturation point of the reinforcement of silica gel into the metal matrix of Al-Si alloy which was found out experimentally. Here the improvement of the mechanical properties of Al-silica gel MMC composite were studied with respect to that of pure Al-Si alloy. Different tests were conducted to show the results. Conventional ingot metallurgy with infiltration technique using vortex method had been employed in the fabrication process. The test results show that there are improvements by 17.14%, 13.46%, 11.48%, and 18.18% on compressive strength, impact strength, Brinell hardness value, and Rockwell hardness no respectively of Al-silica gel MMC over the pure Al-Si alloy. 相似文献
956.
Adhesively bonded composite patch repair has been widely used to restore or extend the service life of cracked structural components due to its effectiveness to mechanical repair technique. In this work, the finite element method is applied to analyse the performance of the bonded composite patch for repairing cracks emanating from semicircular notch root in pure mode II. The stress intensity factor was computed at the crack tip repaired using a boron/epoxy patch for different orientation of fibers, taking into account the disbond. In this case, the increase of a patch thickness reduces the negative effects of disbond. When this effect is significant between the patch and the plate, it reduces the repair effectiveness. The maximum reduction obtained by using a boron/epoxy of fibers in the x-direction is of the order of 20% more important compared to a patch having its fibers in the y-direction. The stress intensity factor exhibits an asymptotic behaviour as the disbond size increases. 相似文献
957.
The adhesively bonded composite patch repair technique has been used to restore or extend the service life of the cracked aluminium structural components because of its efficiency. In this study, the finite element method is used to analyse the performance of the different bonded composite patches at a semicircular lateral notch and the repair of cracks emanating from this kind of notch. The knowledge of the stress distribution in the neighbourhood of the cracks is important for the analysis of their repair according to the geometry of the patch. The effects of the mechanical and geometrical properties on the variation of the stress intensity factor in the crack tip were highlighted. The effects of the adhesive properties and of the patch size on the stress intensity factor variation at the crack tip in mode I were also highlighted. The comparison between the double and single patch repairs is also given in this study. The results obtained show that the stress intensity factor of the crack tip repaired by two composite patches, is reduced to a half compared to the one that is repaired only by one patch. The orientation of fibres possessing a higher rigidity perpendicularly to the crack propagation considerably influences the reduction of the stress intensity factor. The adhesive properties must be optimised in order to increase the performance of the patch repair or the reinforcement. 相似文献
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959.
利用开环正弦波调制解调方法,推导了铌酸锂相位调制器的残余强度调制(简称RIM)对干涉型光纤陀螺(简称IFOG)信号的影响,指出在调制频率漂移或光纤环渡越时间变化时RIM可导致陀螺的零偏和噪声增大.对典型条件的计算表明,0.01°/h的IFOG容许的最大RIM为13ppm,0.1°/h的中低精度IFOG则为81ppm.提出利用锁相放大器精确测量相位调制器RIM的方法,并对国产器件进行测量,结果表明,器件RIM指标可在中低精度IFOG中应用. 相似文献
960.
研究了具有刚性中心的复合材料层合开顶扁球壳在中心集中冲击载荷作用下的非线性动力屈曲问题。通过增加横向转动惯量项得到中心集中冲击下复合材料层合开顶扁球壳非线性稳定性的控制方程,采用Galerkin方法得到以刚性中心位移表达的冲击动力响应方程,并用Runge-Kutta方法进行数值求解,应用Budiansky-Roth准则(简称B—R准则)确定冲击屈曲的临界荷载;讨论了壳体几何尺寸对复合材料层合开顶扁球壳冲击屈曲的影响。 相似文献