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本文用高频响应的热线风速仪及压力传感器作为测量仪器,与磁带记录仪及CF-920动态信号分析仪一起,组成测量及分析系统,并用该系统对离心压气机带叶片扩压器时的流动脉动进行了测量,得出了流体脉动的时间和空间特征.文中给出了失速波形及失速参数随流量的详细变化.本文装置上产生三团失速,流量减小过程中。失速团以2.2%~7%的叶轮转动速度旋转.转速变化时,失速现象的演变过程并不发生变化.失速时,叶片扩压器前缘附近的流动最为恶化,流体脉动幅度较大,气流角的变化剧烈. 相似文献
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The aim of this paper is to investigate the dynamic characteristics of a valve-less micropump. A dynamic mathematical model of the micropump based on a hydraulic analogue system and a simulation method using AMESim software are developed. By using the finite-element analysis method, the static analysis of the diaphragm is carried out to obtain the maximum deflection and volumetric displacement. Dynamic characteristics of the valve-less micropump under different excitation voltages and frequencies are simulated and tested. Because of the discrepancy between simulation results and experimental data at frequencies other than the natural frequency, the revised model for the diaphragm maximum volumetric displacement is presented. Comparison between the simulation results based on the revised model and experimental data shows that the dynamic mathematical model based on the hydraulic analogue system is capable of predicting dynamic characteristics of the valve-less micropump at any excitation voltage and frequency. 相似文献
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基于太阳漫射板的星上定标方法是一种具有高精度、高频次、高效率等优点的独立定标方法,是目前提高我国遥感定标精度的重要手段之一。文章阐述了基于太阳漫射板的星上定标原理、方法及实现过程,建立了空间辐射标准,同时给出了星上反射率定标物理模型。分析定标物理模型发现,影响星上定标不确定度最主要的因素是太阳漫射板BRDF实时量值的确定。为此,首先介绍了星上定标时机的选择,根据所确定定标时机的太阳照明角度对太阳漫射板在实验室相应入射角度下的BRDF进行了测量。通过对太阳漫射板从制作完成到星上使用寿命终结整个过程中各阶段的BRDF量值的监测及修正,确保太阳漫射板定标时刻可为遥感器提供精确已知的辐射输入,实现遥感器全寿命期的高精度星上定标。最后,结合国内对定标模型中相关参数项测量的不确定度水平,按照测量不确定度B类评定的方法对基于太阳漫射板星上定标不确定度进行了预估,可实现星上反射率定标不确定度优于2.03%,绝对辐射定标方法不确定度优于2.04%。 相似文献
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本文试验研究了扩压器几何参数对一高速离心风机的噪声的影响。扩压器的几何参数包括叶片数、叶轮与扩压器的径向间隙和倾斜前缘倾角以及它们的耦合作用对风机噪声的影响。试验结果表明:(1)风机A声级噪声随扩压器叶片数增加而下降,但气动性能也随之下降;(2)扩压器前缘半径从R_3/R_2=1.03增加到1.07,在设计点风机A声级噪声降了约3 dB(A),继续增大至1.09则基本不变;(3)适当倾斜扩压器前缘可有效降低风机噪声,在设计点30°倾角扩压器相应的风机A声级噪声下降了约3.6 dB(A);(4)倾斜扩压器前缘与增大径向间隙的降噪效果不能叠加。 相似文献
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In the present paper, we describe the encryption and decryption of two-dimensional images. The encryption is done by employing a sandwich phase diffuser made by using two elongated speckle patterns, and placed in the Fourier plane of a double random phase encoding system. After encryption, the two constituent phase diffusers of such a sandwich diffuser are separated. During decryption, if the conjugate of either of the two elongated phase speckle patterns is used, the image cannot be retrieved. Correct decryption is also not possible if a sandwich diffuser with any of the phase speckle patterns is shifted in position with respect to the other. For decryption, the encrypted image is Fourier transformed and multiplied by the conjugate of the sandwich diffuser, and then the product is further Fourier transformed. It is possible to generate the image only if both the elongated phase speckle patterns are matched point-to-point and then the proper conjugate is made. The use of elongated speckle patterns in constituting a sandwich phase diffuser makes the system less complicated as compared to the use of a sandwich diffuser made with normal speckle patterns, enabling an easy alignment of the random phase diffuser at the time of rejoining the constituent diffusers for making the right key. The ease of alignment is due to the reduction of the requirement of 360° scanning at the time of rejoining these diffusers with little reduction in the security of the system. Simulation results are presented in support of the proposed idea. For optical implementation, the decrypted image may be obtained by generating a phase conjugate wave by the phase conjugation technique, and passing through the same sandwich phase diffuser. To evaluate the reliability of the technique, mean square error (MSE) between the decrypted and original image has been calculated. 相似文献