Generally, the accuracy of satellite navigation is strongly affected by the deployment of the satellites relative to the user's equipment and also affected by the type of navigation methods to be applied. In the first part of this paper, four types of navigation methods are considered, each of which uses real-ranges, pseudo-ranges or altitude data to determine the position of user's equipments, and then the least-squares method is applied to utilize all measured range data. Next, the expressions for covariance matrices are given in generalized form by which dilutions of precision (DOPs) such as GDOP, VDOP, HDOP and TDOP are derived, and then simplified equations of DOPs are found on condition that the deployment of satellites is in typical geometry. Also, the characteristics of each type of navigation methods is discussed referring to the equations of DOPs derived in this paper, and computer simulation results are added to show the effect of applying the least-squares method and switching the type of navigation method in case that range measurements are not good.
A basic study concerning the structural optimization of a rotor blade subject to steady combined loadings is conducted. The combined loadings are assumed to be composed of distributed axial and lateral loadings which are simulating the centrifugal force and airloadings for a rotor blade in hover. To simplify the problem, the blade is modeled as a cantilevered rotating beam with the plane tapered cross section. The minimum deflection problem of the cantilevered rotating beam is formulated as an optimization problem involving inequality constraints and solved using optimal control methodology. Optimum area distributions are determined numerically for typical combinations of combined loadings and effects of the centrifugal force on the optimum solutions are discussed. Numerical results reveal clearly the important role of the axial loading on the optimum solution and inclusion of the centrifugal force to the structural optimization of the rotor blade should be essential.
The turbulent boundary layer is regarded as a thermodynamically non-equilibrium flow field with dominant dissipative processes. From the thermodynamics of irreversible processes, the rate of entropy production should be minimized in the flow field. Fluiddynamically, some self-organizing mechanism must exit so as to control the energy dissipation respond to the demand of thermodynamics. The first part of the present paper is an extension of the previous one (Aihara, Y.: J. Fluid Mech., 214 (1990)), dealing in more detail with the experimental investigation of the establishment of self-organization in the turbulent boundary layer. The second part of the paper discusses the control of turbulence by means of suction. Suction is considered an effective means of reducing the induced negative normal pressure gradient by turbulence. The experimental results involving the change of the behaviour of turbulence give us a deeper insight into the flow field, especially through the change in Reynolds stress, and at the same time provide useful information for effective turbulence control by using a small amount of suction.
Numerical analyses and experiments of a Hall thruster have been conducted not only to improve thruster performance but also to understand the plasma acceleration processes. 1kW class Hall thrusters were fabricated to measure thrust, ion beam current, and distributions of plasma density, electron temperature, and space potential in the acceleration channel. Two-dimensional ion flow model was made to analytically examine the plasma acceleration processes in the channel, and the analytical results are compared with the experimental ones.