The resonant sensors based on aluminum nitride double-ended tuning fork (AlN DETF) have the characteristics of small size, good stability and reliability, fast response. In order to improve the sensitivity and resolution, it is necessary to analyze the influence of the structure parameters of vibrating beam on the sensitivity and signal power of AlN resonator. The multi-physics model of AlN DETF resonator was established to verify effect of single parameter on the sensitivity by pre-stressed eigenfrequency analysis. The relationships between signal power and length, width of vibrating beam were obtained by post-processing data of simulation results when the thickness remained constant. The results show that relative sensitivity and signal power are growing with opposite direction with the width or the length of the beam. Therefore, there is a design tradeoff between signal power and relative sensitivity of AlN resonator according to the process and structure strength. The optimized AlN DETF resonator was simulated, its sensitivity, signal power and Q are 56 Hz/μN, 6.8e-4 nW and 958, respectively.
This paper presents the design and application of a lever coupling mechanism to improve the shock resistance of a dual-mass silicon micro-gyroscope with drive mode coupled along the driving direction without sacrificing the mechanical sensitivity. Firstly, the mechanical sensitivity and the shock response of the micro-gyroscope are theoretically analyzed. In the mechanical design, a novel lever coupling mechanism is proposed to change the modal order and to improve the frequency separation. The micro-gyroscope with the lever coupling mechanism optimizes the drive mode order, increasing the in-phase mode frequency to be much larger than the anti-phase one. Shock analysis results show that the micro-gyroscope structure with the designed lever coupling mechanism can notably reduce the magnitudes of the shock response and cut down the stress produced in the shock process compared with the traditional elastic coupled one. Simulations reveal that the shock resistance along the drive direction is greatly increased. Consequently, the lever coupling mechanism can change the gyroscope's modal order and improve the frequency separation by structurally offering a higher stiffness difference ratio. The shock resistance along the driving direction is tremendously enhanced without loss of the mechanical sensitivity.
To study the combustion characteristics of turbulent jet flames under different gravity environments, the centerline temperature distribution curve and air entrainment rate of turbulent jet flame from microgravity to hyper gravity was carried out by CFD simulation. Five different gravity values have been considered. The simulation results show that the flame temperature decreases with the increase of gravity in the intermittent flame region and plume region. The maximum temperature decreases with the increase of gravity, while their position decreases accordingly. The evolution of air entrainment has been analyzed under different gravity environments. Based on the hydroxyl concentration distribution, a correlation of flame height has been obtained through dimensionless analysis. The evolution of air entrainment has been described under different heat release rate and gravity environments.
High-pressure, high-speed diesel fuel sprays are complex multiphase flow phenomena. Great efforts have been devoted to understand their dynamics that is essential to the breakup, especially, in this near-nozzle region. However, conventional optical techniques are not effective to probe the dynamics in the first several millimeters of the optically dense region, where liquid is fast and in a complex morphology. By taking advantage of highintensity and high-brilliance x-ray beams available at the Advanced Photon Source (APS), the morphology of the sprays can be imaged with ultrafast x-ray micro-imaging techniques and with sub-ns temporal resolution. Furthermore, two short x-ray pulses (sub-nanosecond to a few nanoseconds) with a variety of intervals can be used to visualize the high-speed sprays. By tracking the movement of features in the double-exposure images without the need of seed particles, it becomes well possible to derive velocity fields of the sprays in the nearnozzle region. To understand near-field flow dynamics of diesel and biodiesel sprays injected at 200 MPa and travelling at a velocity exceeding 600 m/s, double-exposed images were taken using x-ray pulses with time interval of 68 ns. By using auto-correlation analysis, the near-field spray velocity can be obtained quantitatively. We recorded the double-exposed x-ray images and derived auto-correlation functions of diesel and biodiesel sprays under various injection pressures up to 200 MPa. We note that 200 MPa injection pressure is not the maximum limit for the x-ray method rather it was limited by the specification of the fuel-injection system. The theoretical velocity was calculated using Bernoulli equation, which was compared against measurement. The results showed that the axial velocity increased with increase in injection pressure and reached over 600 m/s at 200 MPa injection pressure. We also made comparison between diesel and biodiesel sprays under various injection pressures. To probe the interaction between the sprays and surrounding gas, the local flow velocities were measured at different axial and radial locations. The results will prove valuable in providing validation of internal-flow and spray modeling.
Surface reconstruction technology needs to fit the collected point cloud data into an expression with a complete base function. How to improve the fitting accuracy of surface reconstruction is the focus of this research. In this paper, aiming at the surface fitting model based on Gaussian radial basis function(RBF), the influence of shape factor selection on surface fitting accuracy is studied, and a new method for calculating RBF shape factor is proposed. The shape factor is connected with the size of the surface to be fitted, which strengthens the relationship among the kernels. Taking the given point cloud data as an example, the simulation experiments were carried out, and the fitting accuracy of different shape factors was compared, and the curved surfaces of different shapes were fitted. The results show that the accuracy of surface fitting can be improved by choosing shape factor combined with the size of fitting area; surface fitting based on RBF is suitable for the surface with small curvature and gentle surface; RBF can be used for the description of non-rotational symmetric surface, but the fitting accuracy will decrease.
An optimized design of accelerometer was presented for the UV-LIGA process in this paper. Based on the FEA simulation of mechanical property and developing process, traditional comb-finger accelerometer was optimized for UV-LIGA process. The Finite Element Analysis (FEA) result of mechnical property demonstrates that the novel design offer the 2.96 times in sensitivity. Moreover, novel structure makes the hydrodynamics property during the developing process much better than that of traditional structure. It is great characters for the precision developing result and quality manufacture.
This paper presents the design and analysis of a novel dual-mass microelectromechanical systems (MEMS) resonant output gyroscope (ROG), which can effectively eliminate the influence of common-mode disturbance, such as the linear acceleration, on the gyroscope working mode by the design of dual-mass form, as well as on the frequency outputs of the double-ended tuning fork (DETF) resonators by the differential arrangement. The concept of the ROG is introduced first. Then the dynamics of the gyroscope and the force-frequency characteristics of the DETF resonator are theoretically analyzed. By establishing the distribution coefficient of force and the reasonable equivalent of the force-frequency characteristics of the DETF resonator, the accurate expression of the device sensitivity is obtained. Based on the analysis results, the leverage mechanism and the DETF resonator are designed in detail. Then the configuration of the gyroscope, a dual-mass structure, is given. Finally, the validity of the analysis and design are verified by numerical simulations.
With the rapid development of space science and technology in the world,aerospace activities which used to be led by the government become gradually and comprehensively commercialized.Trade rules for aerospace products are gaining more and more attention all over the world.After a long period of development and improvement,the European aerospace products trade control system formed earlier has basically developed a relatively loose system with obvious regional characteristics and higher degree of legalization.China should draw lessons from the successful experience of the European Union,realize the standardization of dual-use products trade,actively participate in multilateral export control mechanism,design of aerospace products international trade operation,and accelerate the space trading system of the legal process,in order to become invincible in the continued development of spaceflight enterprise.
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