共查询到20条相似文献,搜索用时 46 毫秒
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介绍了一种基于时延向量的DOA估计算法,在对算法误差分析基础上,提出了一种DOA估计可靠性准则。利用该可靠性条件,能够方便判定DOA估计的可靠程度,将其应用到多DOA交叉定位试验中,能够有效避免目标位置估计出现野值。 相似文献
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介绍了一种基于单个三维矢量水听器对水面目标进行跟踪定位和运动速度估计的简单方法。首先利用平均声能流法得到目标波达方向的极大似然估计;当矢量水听器深度已知,由目标波达方向的估计序列可得到目标空间位置和运动速度的估计序列。但随着信噪比的降低,目标定向性能随之下降,导致目标位置和速度的估计误差急剧增大。针对直线运动目标,提出利用线性最小二乘法进行目标轨迹拟合的改进算法。仿真结果表明,拟合算法大大提高了目标定位精度和运动速度估计精度,增强了基于单矢量水听器的水面目标运动分析的结果的可靠性。 相似文献
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论文从实时性、可靠性、网络传输能力等方面提出了评价IP网络性能的关键指标,探讨了IP网络性能测试的相关技术和实现方法,为精确定量地评估IP网络的性能、降低网络风险并提高网络服务质量提供了有效的支持。 相似文献
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在对多种可应用于VMIMO-OFDM系统的频偏估计方法的性能和效率进行分析的基础上,针对基于VMIMO-OFDM的无线传感器网络中的精频偏估计问题,提出了一种在频域进行频偏估计的算法.同时,针对基于VMIMO-OFDM的无线传感器网络应用于瑞利衰落严重的环境时不同的导频子载波上频偏估计的误差差异较大的问题,提出了一种基于信道统计信息(CSI)加权的精频偏估计算法,该方法对各个子载波上的频偏估计结果进行加权平均,可使估计误差最小化.理论分析和仿真结果均表明,新提出的算法在高斯信道和多径信道中均有更优的性能. 相似文献
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二维波达方向(Direction of Arrival,DOA)估计是智能天线技术中的一个关键问题.在低信噪比、低快拍数条件下,常规DOA估计算法的性能会严重下降.针对此问题,提出了一种基于均匀面阵的酉ESPRIT算法.算法将复矩阵转化为实矩阵计算,使运算复杂程度简化,估计精度提高,且可实现参数自动配对,是一种比较高效的DOA估计算法.计算机仿真结果表明了所提算法在测向性能方面比常规DOA估计算法有更好的估计性能,且在低信噪比和低快拍数条件下估计性能不受影响,同时具有更小的运算量. 相似文献
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本文介绍了配电网可靠性评估的算法,其中包括基本的解析法、模拟法及后来发展的人工智能方法。同时介绍了改进算法。阐述了各自的应用情况及优缺点。并简单介绍了配电网可靠性的评价指标。最后为配电网可靠性的未来发展做了简单的展望。 相似文献
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在线健康检查中,当应用实测振动数据时,如何处理由实测数据引起的不确定性则成为关键问题之一。文中建议和发展了结构健康检查的区间理论,并用实例介绍了健康检查的具体过程。由测试数据得到健康特征量,并以区间量或区间向量形式给出,是健康特征量的非概率建模。健康特征量的估计过程是区间估计问题,估计过程遵循区间算法,它适合于处理非线性问题。以一栋新建5层楼房的抗震性能评估为实例,介绍了评估过程中区间量的表示方法及区间评估准则。用第一层层间刚度系数为健康特征量,用地脉动的测试数据估计第一阶模态频率和振型的区间上限和下限,由于测点的限制,完整的振型与健康特征量一起被估计,并用层间刚度系数的区间值进行抗震评估。 相似文献
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《International journal for numerical methods in engineering》2018,113(9):1488-1506
In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method. 相似文献
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A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa. 相似文献
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On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.…… 相似文献
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Standards are the basis for production enterprises to organize production ex-factory inspection trade 《中国标准化(英文版)》2008,25(1):24-25
Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.…… 相似文献
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A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils. 相似文献
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C. Qihong W. Zhan‐Wen J. Yi J. Yehua L. Fei F. Hanguang 《Materialwissenschaft und Werkstofftechnik》2014,45(7):582-590
In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M2(B,C), (W,Mo)2(B,C), M3(B,C), M23(B,C)6 type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm2. The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K1 mill housing of bar mill. 相似文献
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Dimiter Hadjistamov 《材料科学与工程:中英文B版...》2019,(2):56-65
The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ... 相似文献
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Kyo-Hong CHOI Kwon-Koo CHO Gyu-Bong CHO Hyo-Jun AHN Ki-Won KIM Yoo-Young KIM 《材料科学与工程学报》2007,25(6):886-891
Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD. 相似文献
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Cubic boron nitride(c-BN) film was deposited on a Si (100) substrate by the RF-magnetron sputtering.The mainly problems for fabrication of c-BN films are the low purity and high intrinsic compressive stress. In order to solve the two problems, the c-BN film with the buffer interlayer was deposited on the substrate which had been implanted with nitrogen and/or boron ions. The results show: the implantation of nitrogen ions can obviously increase c-BN content and reduce the internal stress slightly; while the implantation of boron shows no obvious improvement to the content of c-BN, which can reduce the internal stress in the film obviously. In addition, it is suggested that the implantation of nitrogen and boron shows the best result, which not only can increase the content of c-BN, but also reduce the internal stress in the c-BN film obviously. 相似文献