The acoustic treatment with a rather large cavity was discussed from both aspects of analysis and experiment for low-frequency noise reduction in a low-speed axial flow fan. The rectangular and annular ducts with treatments were used. It is tentatively concluded that the axial modes of sound wave travelling in the cavity played an important role in low-frequency noise reduction mechanism. The acoustic treatment with a biased cavity showed a promise from a view point of weight reduction in aeroengines and fluid machinery.
The laser propulsion is expected to be one of the next-generation space propulsion systems. It is important to analyze the mechanism of LSD (Laser-Supported Detonation) waves, which are caused by laser absorption. The performance of laser propulsion is determined mainly by laser absorption efficiency. At high temperatures where LSD waves are produced, the characteristic physical phenomena of LSD take place in a narrow ionized absorption layer. The most important phenomenon is the inverse bremsstrahlung, a key mechanism in laser absorption: The laser energy is transformed into the kinetic energy of free electrons by photon absorption during electron-ion/neutral collision, which is re-distributed among heavy particles through collisions. Thus, the number density of free electrons is essential to the problem. In this paper, we have generated such an LSD wave by solving an unsteady nonequilibrium 3-dimensional flowfield, taking account of atomic/molecular processes occurring in an Argon plasma consisting of Ar, Ar+ and e- As a numerical method, we have used a modified Harten-Yee-type TVD scheme. Detailed discussions are given on the mechanism of 3-dimensional axisymmetric LSD propagation.
In this paper, the mission profile for a small satellite assumed to be launched as a piggyback payload is analyzed. In this mission, a wake, which is a high vacuum region formed behind satellites orbiting in Low Earth Orbit (LEO), is used in order to isolate an object from the disturbances of the thin atmospheric stream. As preliminary research on the use of this wake as a micro gravity experimental environment, the motion of a ball which is launched by an orbiting satellite into the wake is analyzed. The ball is treated as a free-flying payload. Using the trajectory of the free-flying payload, an estimation method for both atmospheric density and the attitude angles of the satellite is proposed, analyzed, and validated with simulations. An extended Kalman filter is used to derive the estimation. Advantages and limitations of the method are discussed.
A control method of a free-flying robot, which can be described in unified form, to capture a floating object is presented. The control law is based on a resolved acceleration scheme and uses adaptive control when the mass of the floating object is unknown. This control method can be used whether the actuators to propel the robot (e. g., thrustors) are utilized or not. To control the robot rotation about one axis, a new orientation parameter is introduced. To demonstrate the proposed control method, numerical simulation is conducted. It is proven that the control method can be applied to all steps in the capturing maneuver of the floating object.
Main requirements for the flight control system are desirable response and robust stability. Eigenstructure assignment (EA) is one of the approaches which achieve the desirable response. EA is based on the state feedback and some methods of designing the output feedback laws are proposed, but their output feedback laws have no guarantee for the robust stability. By the way, the quadratic stabilization (QS) has been often used to solve the robust control problem with structured uncertainty and disturbance attenuation. In this paper, we propose the 2-step approach which combines QS with EA. That is to say, at first step, a state feedback control law which achieves the desirable response is solved by EA. Next, a state estimator which has robust stability against both structured uncertainty and unstructured uncertainty is designed by QS with disturbance attenuation. Moreover, this new approach is applied to two examples of a longitudinal and a lateral-directional flight control, as a result it is shown that the designed control laws give the good performance and robustness.
We performed a highly-efficient numerical analysis for a plasma flow in an MPD thruster, using an explicit upwind-TVD scheme and a generalized coordinate system. The plasma gas was treated by a one-fluid model with the corresponding MHD equations. The plasma entered the thruster with the sonic speed, generating the phenomena characterized by such a flowfield. To accelerate the calculation, the steady equations were found enough to calculate the electromagnetic field, giving quick convergence to a steady solution with its associated eigen values.
The aerodynamic characteristics of 2-dimensional airfoils in proximity to the ground are examined. The purposes of this paper are: 1. aerodynamic research of the steady pressure distribution in proximity to the ground, 2. suggestion of the methods to simulate the ground effect and 2-dimensionality in the wind tunnel testing, 3. examination that it is reasonable to use the finite difference method based on the small perturbation velocity potential equation in the ground effect problem. The pressure distribution changes according to the height, the ways of which are different between a flat plate airfoil and a NACA0012 airfoil. The effect of viscosity is also examined through numerical calculations.
The velocity of a metastable argon flow was measured by means of laser induced fluorescence (LIF). A commercial laser diode was employed as the diagnostic instrument. The transition between 1 s5 and 2 p6 was available for LIF and the resultant fluorescence in a vacuum ultraviolet range was detected by an electron multiplier. The velocity of the argon flow estimated at 750m/s and its number density ranged around 103 particles per cm3.