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831.
《中国航空学报》2023,36(1):468-479
The double-sided incremental forming (DSIF) improved the process flexibility compared to other incremental sheet forming (ISF) processes. Despite the flexible nature, it faces the challenge of low geometric precision like ISF variants. In this work, two strategies are used to overcome this. First, a novel method is employed to determine the optimal support tool location for improving geometric precision. In this method, the toolpath oriented the tools to each other systematically in the circumferential direction. Besides, it squeezed the sheet by the same amount at the point of interest. The impacts of various support tool positions in the circumferential direction are evaluated for geometric precision. The results demonstrate that the support tool should support the master tool within 10° to its local normal in the circumferential direction to improve the geometric accuracy. Second, a two-stage process reduced the geometric error of the part by incrementally accommodating the springback error by artificially increasing the step size for the second stage. With the optimal support tool position and two-stage DSIF, the geometric precision of the part has improved significantly. The proposed method is compared to the best DSIF toolpath strategies for geometric accuracy, surface roughness, forming time, and sheet thickness fluctuations using grey relational analysis (GRA). It outperforms the other toolpath strategies including single-stage DSIF, accumulative double-sided incremental forming (ADSIF), and two-stage mixed double sided incremental forming (MDSIF). Our approach can improve geometric precision in complex parts by successfully employing the support tool and managing the springback incrementally. 相似文献
832.
The effect of gain-phase perturbations and mutual coupling significantly degrades the performance of digital array radar (DAR). This paper investigates array calibration problems in the scenario where the true locations of auxiliary sources deviate from nominal values but the angle intervals are known. A practical algorithm is proposed to jointly calibrate gain-phase errors and mutual coupling errors. Firstly, a simplified model of the distortion matrix is developed based on its special structure in uniform linear array (ULA). Then the model is employed to derive the precise locations of the auxiliary sources by one-dimension search. Finally, the least-squares estimation of the distortion matrix is obtained. The algorithm has the potential of achieving considerable improvement in calibration accuracy due to the reduction of unknown parameters. In addition, the algorithm is feasible for practical applications, since it requires only one auxiliary source with the help of rotation platforms. Simulation results demonstrate the validity, robustness and high per-formance of the proposed algorithm. Experiments were carried out using an S-band DAR test-bed. The results of measured data show that the proposed algorithm is practical and effective in appli-cation. 相似文献
833.
针对某型飞机在地面低速试滑中出现的侧偏故障进行了探讨,在大量惯性台模拟试验的基础上,对侧偏发生的原因、机理进行了分析,提出了解决侧偏故障的措施。 相似文献
834.
835.
一种复合型垂直轴风力机实验研究 总被引:1,自引:0,他引:1
提出了一种升阻复合型垂直轴风力机,并对该风力机进行了实验研究。首先通过改变叶片安装角,对不同风速下风力机的性能进行实验研究。其次对叶片进行正装和反装对比实验。实验结果表明,当叶片反装时,在同一风速下安装角为-6°时功率最大,此外对安装角为-6°时的多个风速进行实验研究,发现随着风速的增大,每个风速下的最大功率增大。 相似文献
836.
MPEG-4是一种面向多媒体的压缩编码标准,运动补偿是MPEG-4视频压缩编码标准中的一种重要算法,本文讲述了在DSP TMS320C6201上快速实现MPEG-4运动补偿的方法,并给出了测试结果。该算法的设计思想也适用于MPEG-1、MPEG~2和H.263等视频压缩标准。 相似文献
837.
Orbital debris environment models are essential in predicting the characteristics of the entire debris environment, especially for altitude and size regimes where measurement data is sparse. Most models are also used to assess mission collision risk. The IDES (Integrated Debris Evolution Suite) simulation model has recently been upgraded by including a new sodium–potassium liquid coolant droplet source model and a new historical launch database. These and other features of IDES are described in detail. The accuracy of the IDES model is evaluated over a wide range of debris sizes by comparing model predictions to three major types of debris measurement data in low Earth orbit. For the large-size debris population, the model is compared with the spatial density distribution of the United States (US) Space Command Catalog. A radar simulation model is employed to predict the detection rates of mid-size debris in the field of view of the US Haystack radar. Finally, the small-size impact flux relative to a surface of the retrieved Long Duration Exposure Facility (LDEF) spacecraft is predicted. At sub-millimetre sizes, the model currently under-predicts the debris environment encountered at low altitudes by approximately an order of magnitude. This is because other small-size debris sources, such as paint flakes have not yet been characterised. Due to the model enhancements, IDES exhibits good accuracy when predicting the debris environment at decimetre and centimetre sizes. Therefore, the validated initial conditions and the high fidelity future traffic model enables IDES to make long-term debris environment projections with more confidence. 相似文献
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840.
谭春晓 《沈阳航空工业学院学报》2005,22(1):29-31
根据公差项目的特征要求,对某产品零件孔系加工的生产实际进行了工艺分析,对造成零件孔系加工误差的各项因素进行了定性和定量分析,找出了造成误差的根本原因是工艺装备结构设计带来的系统误差过大和加工工艺方法的缺陷的影响。在此分析的基础上对工艺装备的设计进行了改进,并对加工工艺进行了相应的调整,达到了预期的加工目的。这种技术工作方法,对生产现场的工程技术人员来说是基本要求,也是解决机械制造工艺问题的有效途径。 相似文献