The singular perturbation approach is applied to the longitudinal motion of airplanes, whose linearlized model has well known two-time scale structure in the presence of a slow (phugoid) mode and a fast (short-period) mode. Such a linearlized model is transformed into the singularly perturbed form via scaling of the state. First the flight control systems are separately designed for each mode via state feedback. Then the slow and fast designs are composed, and are applied to the full model. The composite flight control systems are shown to guarantee the damping ratio and the characteristic frequency specified by JIS W 0402.
Spark-tracer technique using glow discharge is presented to measure velocity profiles across boundary layers around models in hypersonic flows. At first, a high voltage and high frequency discharge circuit and a discharge electrodes system used in the measurement are described. Next, to demonstrate the capability of the technique, the measurement of a velocity profile across a flat plate boundary layer is performed. The experimental result agrees well with the computational one based on the Navier-Stokes equations. Moreover, to clarify characteristics of the high frequency glow discharge generated in hypersonic flows, discharge gap voltage and current measurement is carried out and the follows are concluded. A positive column region is used as a tracer in the technique. Its characteristics are affected by retained ions in the column and also by the column length. Finally, from the fact that the experimental and numerical velocity profiles agree well, we may conclude that 1mJ of electric energy which is released in an impulsive discharge does not disturb the flow.
This paper will examine the applicability of the hypervelocity collision model included in the NASA standard breakup model 2000 revision to low-velocity collisions possible in space, especially in the geosynchronous regime. The analytic method used in the standard breakup model will be applied to experimental data accumulated through low-velocity impact experiments performed at Kyushu Institute of Technology at a velocity about 300m/s and 800m/s. The projectiles and target specimens used were aluminum solid balls and aluminum honeycomb sandwich panels with face sheets of carbon fiber reinforced plastic, respectively. Then, we have found that a kind of lower boundary exists on fragment area-to-mass distribution at a smaller characteristic length range. This paper will describe the theoretical derivation of lower boundary and propose another modification on fragment area-to-mass distribution and it will conclude that the hypervelocity collision model in the standard breakup model can be applied to low-velocity collisions possible with some modifications.
Lamb waves can propagate for long distance and change its waveform depending on the existence of damages within the propagation path. Hence, from the change in the waveform, the damages inside a structure can be detected. In this research, a new health monitoring system using piezo-actuators and fiber Bragg grating (FBG) sensors was developed. Piezo-actuators on the surface of a composite laminate generate Lamb waves into the laminate. Then the propagated waves were received by FBG sensors attached on it. From the change in the waveform, damages are detected. As preliminary researches, the appropriate gauge length of the FBG sensor for receiving Lamb waves was determined by theoretical calculations and experiments, and the directional sensitivity of the FBG sensor was evaluated. Then the authors succeeded in detecting a delamination in a CFRP cross-ply laminate by monitoring the change in the waveform received by an FBG sensor.
Effects of streamwise vortex inducement on growth of a compressible double shear layer are investigated experimentally. Air is injected with a subsonic speed into a co-flowing supersonic air stream in the parallel direction, forming a compressible double shear layer. The Mach numbers of the subsonic and supersonic air streams are 0.29 and 1.78, respectively. The convective Mach number is 0.62. Several types of sine-curved trailing edges are used to induce streamwise vortices into the shear layer. The amplitude, wavelength and phase of the sine curve are varied widely. It is shown that the growth of the streamwise vortices is determined by their spacing. For the symmetric sine-curved trailing edges, the streamwise vortex inducement has no effect on the growth rate of the shear layer. For the asymmetric sine-curved trailing edges, with the increase in the streamwise vortex intensity, the growth rate of the shear layer is increased. At the maximum, 90% enhancement in the mixing is achieved when compared with the straight trailing edge.
Characteristics of a secondary instability in a compressible double shear layer are investigated, using a two-staged linear stability analysis. By superimposing a small disturbance onto a basic flow, the temporal growth rate and eigenfunctions of the disturbance are investigated. Vortex evolution by flow instabilities is shown as follows: (i) Due to a flow instability, a disturbance is amplified and spanwise organized vortices are formed (Primary instability). (ii) As the spanwise vortices grow, a new instability appears and the vortices are distorted periodically (Secondary instability). It is shown that, in the secondary instability, there are two dominant modes of the disturbances, since there are upper and lower shear layers. It is shown that, in the secondary instability, the temporal growth rate of the disturbances has the maximum value, when the scale ratio between the secondary and primary instabilities is 0.7, and that the maximum value of the temporal growth rate is almost the same as that of the primary instability.