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As the main standard flowmeter, Sonic nozzle has been widely used in aerospace, petrochemical and biomedical fields. Recently, a number of studies have been conducted on small-scale sonic nozzles. Since the standard ISO sonic nozzle is difficult to process at a small scale, the geometry of the shrink nozzle, the diffusion nozzle and the conical venturi nozzle is proposed based on the circular ISO nozzle, and the geometric structure and shape flow to the nozzle. A preliminary analysis of the effects of the characteristics was carried out. In this paper, the computational fluid dynamics method is used to numerically simulate the flow field inside the three sonic nozzles. The influence of the geometry of the constricted section, the throat and the diffusing section on the nozzle flow characteristics is analyzed and compared with the annular ISO nozzle. In contrast, the flow characteristics of four kinds of microsonic nozzles are compared. Considering the feasibility of actual processing, the geometric structure with better discharge coefficient and critical back pressure ratio is obtained, which provides a reference for the development of micro nozzles.

This paper proposes a novel diving plane control scheme for autonomous underwater vehicle (AUV) based on tracking differentiator (TD) and cascade control (CC). The outer loop controller and inner loop controller adopt PI and P, respectively. Firstly, the mathematical model of AUV is established. The model consists of two parts: one is the depth model, and the other is the pitch model. Then, both controllers are designed by using CC with the tracking differentiator. The TD can filter the white noise of input signals and make the noise have little influence on control performance. Simulation results demonstrate the effectiveness of the proposed method.

Electromagnetic compatibility is essential to airborne device.It is directly related to the normal and safe operation of the whole aircraft system.The integrated electromagnetic environment was introduced for the airborne optical imaging and measurement system.Some effective measures were adopted,such as reducing interference source,sorting cables,improving ground system,shielding technology,optimizing the wiring structure of the circuit board and so on,so that the airborne optical imaging and measurement system met the electromagnetic compatibility requirement of the industry standards.All equipment can operate normally,ensuring the safety of the whole aircraft system.

A circular polarized microstrip antenna with a working frequency of 6.26 GHz was fabricated from YBCO HTS films. The transmission coefficient and circular polarization ratio of the antenna at different external magnetic field B were measured at 4.2 K. The experimental results showed that its transmission coefficient and circular polarization ratio hardly changed with B up to 1 T. It is concluded that the field-induced increase of surface resistance of YBCO films would not influence the microwave properties of this antenna at B ⩽ 1T and T = 4.2 K.