Thermal cycles of a turbofan jet engine equipped with an intercooler are optimized for two different engine sizes to understand the engine characteristics. The optimization tool consists of a thermodynamic cycle analysis module, a weight evaluation module, a heat exchanger model and an optimization routine. It is confirmed that the tool searches for a reasonable design point within a ten-dimensional design space. The pressure ratio of a conventional turbofan is restricted by the compressor exit temperature. In contrast, intercooling enables higher pressure ratios and hence higher core thermal efficiency. The net decrease in fuel consumption is small however, because the thermal efficiency improvement, weight penalty and pressure loss are all at the same order of several percent. The minimum blade height at the compressor exit imposes another restriction on the pressure ratio increase for small intercooled engines, and net fuel consumption in small engines may increase by intercooling. The performance of an intercooled turbofan is determined by a balance between thermal efficiency improvement through the increase in pressure ratio and disadvantages resulting from additional weight and pressure losses. The development of a light, low-pressure-loss heat exchanger and optimization of the thermodynamic cycle are important.
The frequency of acoustic sound emanating from the trailing edge of a two-dimensional airfoil is known to exhibit a ladder-like variation, displaying discontinuous jumps between discretely identifiable states as the free stream velocity varies. In order to reveal the underlying causes for this behavior, a two-dimensional jet issuing into still air with no aerodynamic sound emission is used as a model platform to study this phenomenon, because prescribed aero-acoustic sound may be readily introduced into the flow at the jet exit. When unstable disturbances growing in the shear layer of the jet are excited by a loudspeaker, an acoustic feedback loop automatically selects one frequency from the unstable frequencies present in the shear layer, and the resulting ladder-like variations are found to be similar to those present in airfoil trailing-edge noise. In addition, the observed slope of each rung of the ladder in the selected frequency behavior, and the observed jump frequency between ladder steps, show good agreement with existing empirical models. It is also discovered that when the remainder of the distance between the speaker and jet divided by the wavelength of the selected acoustic sound is equivalent to one-half wavelength of the accepted sound, the selected frequency jumps to another state.
The whole-spacecraft vibration isolation (WSVI) platform can enhance the dynamic environment in the launch loads of rocket launchers during trips into orbit. In this dissertation, non-probabilistic reliability research is conducted for the dynamic characteristics of the integrated active and passive WSVI platform. First, the non-probabilistic reliability theory of the uncertain integrated active and passive vibration isolation system is established. Then, through the first-order equivalent dynamics model for the integrated active and passive WSVI system, the non-probabilistic reliability analysis of the WSVI platform is conducted. Finally, the analyzed accuracy of the non-probabilistic reliability for the WSVI platform is tested by experiments, through which the reliability and security of the integrated active and passive WSVI platform launch are enhanced.
A new type of strain sensor using a CMOS inverter oscillator circuit has been developed. This sensor does not require an amplifier because a counting device measures the frequency changes in the circuit voltage output caused by the resistance changes in the strain gauge. The characteristics and measurement accuracy of the sensor that consists of an oscillator circuit and a strain gauge are confirmed by static tensile tests of specimens. The test results reveal that the same level of accuracy as that of a conventional sensor is achieved by using a simple compensation factor assuming the existence of an internal resistance on the circuit.
A new solar sail orbit control strategy is proposed for the solar sail halo orbit mission. The reflectivity control device, initially developed for attitude control, is utilized to control the solar sail orbit by switching the states between absorption and specular reflection. The solar radiation pressure force of a solar sail equipped with reflectivity control devices is modeled, and can be changed continuously by adjusting a continuous variable associated with the reflectivity control device. This model is used to study the artificial Lagrange point and periodic orbit around it in the restricted three-body problem. The dynamical equations of motion are linearized around the periodic orbit, and linear quadratic regulator and Floquet theory are utilized to design the control law for the linear time-periodic system. Utilization of attitude adjustment is a way to control the orbit of the solar sail without reflectivity control devices. In this paper, the reflectivity control device is used to stabilize the periodic orbit without attitude adjustment. The results based on attitude adjustment and reflectivity control devices are compared. The simulations indicate that the strategy using reflectivity control devices is more robust with respect to initial errors.
In order to achieve precise maneuvers of formation flying satellites, an accurate and controllable relative motion model is greatly needed. However, most transformation equations only take either external disturbances or J2 perturbation into consideration, which will affect satellites' long-term reconfiguration. Therefore, nonlinear relative motion equations of satellites in elliptic orbits with consideration of both external disturbances and J2 perturbation are derived in this paper. To obtain accurate formations and improve the system robustness in the presence of external disturbances and J2 perturbation, a reconfiguration and formation-keeping control law based on the nonlinear sliding mode function is proposed, where nonlinear gains of exponential growth are used to replace the constant gain of the traditional sliding mode function. The proposed control law restrains the control law saturation during big errors and improves the response rate during small errors, and effectively enhances the rate of reaching the sliding mode surface. Finally, the numerical simulation results verify the effectiveness of the proposed strategies.
This paper provides a new method for robust spacecraft attitude estimation in the presence of measurement biases. The proposed method is developed based on the separate-bias or two-state Kalman filter which was first introduced by Friedland. The separate-bias Kalman filter consists of two stages: the first stage, the "bias-free" filter, is based on the assumption that the bias is nonexistent; the second stage, the "bias" filter, is implemented to estimate bias vectors. The output of the first filter is then corrected with the output of the second filter. In this research, the authors propose a real-time tuning method for a parameter in the Kalman gain calculation process of the "bias" filter. The adaptive scale factor is optimized relying on the minimization of the cost function, which is calculated from the difference between the predicted and measurement values. The proposed filter has a faster convergence speed from large initial errors and an increased accuracy on unpredicted bias models than conventional methods. Moreover, to verify these advantages, the research also provides analyses and comparisons between the proposed method with conventional methods like the original separate-bias Kalman filter, unscented Kalman filter and extended Kalman filter in several numerical simulation scenarios for a microsatellite.