The transitional flight of a helicopter from the high speed trim flight to the hovering flight at low altitude was analyzed. Linear equations of motion at four trim flights were basically used. Some Fuzzy Models were analyzed to express equations of motion of a helicopter between these trim flights by applying the membership function. The control system for automatic landing was determined by the LQ Regulator method based on the Fuzzy Model. Stability and control derivatives including the control system between these Fuzzy Models were also interpolated by applying the membership function to adjoining equations of motion. Transitional flights of a helicopter expressed by these Fuzzy Models were analyzed, and compared with results obtained by the basic equations of motion. Results showed that the Fuzzy Model was considered to be useful to express the non-linear equations of motion of the transitional flight of a helicopter.
The numerical method to solve simultaneous design and control optimization problems is considered. Firstly, the simultaneous optimization problem dealt with in this paper is defined, and this problem is transformed into a new formulated nonlinear programming problem. Considering that the nonlinear programming problem is solved by using a sequential quadratic programming method, the diagonal form of the Hessian matrix for the Lagrange function is introduced in a new formulation named Block Diagonal Hessian (BDH) method. Secondly, the BDH method is applied to the simultaneous spaceplane design and trajectory optimization problem, where the best size and its optimal trajectory are estimated to realize it. Through the several calculations, it is confirmed that the proposed BDH method is effective for simultaneous design and control optimization problems.
The impingement of a streamwise vortex on a fin is investigated experimentally with high-image-density particle image velocimetry (PIV) and dynamic pressure transducers in order to relate the structure of vortex breakdown to the spectra of surface pressure along the fin. The instantaneous and ensemble-averaged distributions of vorticity from PIV show strong concentrations of vorticity along the edges of the breakdown region. Correspondingly, the amplitude response of the pressure spectra is the strongest when the fin is located near the edge of vortex breakdown. The dominant frequency of the surface pressure is insensitive to cross-stream displacements of the vortex axis relative to the leading-edge of the fin. Spectra of surface pressure at crucial locations on the fin are related to these features of the instantaneous and averaged flow structure.
The constitutive relationship of silicon nitride ceramics at elevated temperature is described by a linear viscoelastic relation. The viscoelastic behavior of silicon nitride ceramics is idealized by a composite sphere model in which the crystalline and the amorphous phases are simplified as elastic and Maxwell bodies, respectively. In the model, a two-parallel-Maxwell-body model is obtained by the elastic-viscoelastic correspondence principle. The elements in a two-parallel-Maxwell-body model correspond to the crystalline and the amorphous phases in the material. However, as to the viscous element, only one independent parameter is included. In this paper, parameters of the two-parallel-Maxwell-body model are determined by the experimental result of internal friction of silicon nitride ceramics at different temperatures, and the experimental result is compared with calculated one.
The turbulent separated and reattaching flow formed over a backward facing step has been measured to investigate the unsteady phenomenon of the flow. Upstream of the reattachment point, the power spectrum analysis of the velocity fluctuation indicated the dominant frequency is shifting towards lower frequency, which is thought to be caused by the vortex pairing inside the shear layer. The velocity fluctuation with higher frequency and with larger amplitude is periodically observed at the shear layer edge near the reattachment point. When this fluctuation is observed, the smoke wire visualization picture showed that there is a kind of large smoke cluster downstream of the reattachment point.