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Introduction
Remote sensing satellites play an important role in urban planning and other fields, not only widely used in the civilian field, but also in the military field. Modern high-resolution satellites require extremely high pointing accuracy and stability, especially the need to monitor the satellite's tiny angular vibrations in orbit in real time.
To meet this need, the researchers proposed a micro-angle vibration sensor based on magnetohydrodynamics. This sensor has a variety of advantages, including no mechanical wear and friction damping, small and delicate, high precision, independent of cross-axis, wide response frequency band, etc., it can effectively measure the small angular vibration of satellites in harsh environments.
However, in the deep space environment, gas spills in satellite materials and structures are a common phenomenon that has an important impact on the normal operation of satellites. The main causes of air bubbles in conductive fluids include the suction characteristics of the material, the dissolved gas characteristics of the material, and the surface process characteristics. These factors cause bubbles to form in the conductive fluid, which in turn affects the performance of MHD sensors.
First, the working principle and output model of MHD sensor
The working principle of MHD sensors is as follows: in a ring channel, filled with high conductivity magnetic conductive fluid, the inner and outer surfaces of the channel are made of insulating materials with small friction coefficients, and there are metal electrodes with high conductivity at the upper and lower ends. Through the magnetic field generated by the permanent magnet, the fluid ring is connected to the permanent magnet, so that the magnetic field is perpendicular to the surface of the fluid ring. When the sensor is excited by angular vibration, the conductive fluid remains stationary relative to the fluid ring wall, resulting in induced electromotive force.
In a non-inertial coordinate system, the motion of conductive fluids and electromagnetic fields follows certain equations. However, the presence of bubbles distorts the electric field distribution and affects the output potential of the fluid ring. When bubbles move in a conductive fluid, they are affected by forces such as shear, dragging, and dynamic pressure, which are related to the relative velocity of the bubble to the conductive fluid.
With the increase of the angular vibration frequency, the influence range of bubble convection field and electric field gradually decreases, and the bubble is stretched in the direction of the magnetic field at high frequencies, but the change in the axial direction is small.
2. Simulation and result analysis
We used ANSYS Workbench to build a simulation model that simulates the structure of fluid rings and defines various boundary conditions. In the simulation, we consider the gas content in the conductive fluid and solve the output of the MHD sensor by the magnetic potential method. The results show that an increase in the gas content leads to increased scale factor fluctuations in the sensor and poor test repeatability.
At the same time, linearity is also affected by the gas content, which deteriorates as the gas content increases. In the absence of bubbles, the flow and electric field distributions of fluid rings are regular, but the presence of bubbles distorts the distribution of these fields, causing shifts and distortions.
3. Test and result analysis
We prepared and tested four MHD sensors with different gas content. The results show that the gas content has no significant effect on the static noise of the sensor, but does affect the scale factor, repeatability, and linearity. When the gas content is low, the performance of the sensor is better, but as the gas content increases, the performance gradually decreases.
conclusion
Based on the above results, it can be concluded that when the gas content in the conductive fluid is low, the gas has less influence on the performance of the MHD sensor, which can meet the practical application needs. By reducing the gas content, the accuracy and stability of the sensor can be improved, which has positive guiding significance for the design and process control of the sensor. Therefore, in the development of satellite technology, the research and improvement of MHD sensors are still of great significance.
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