The potential flow of an incompressible fluid through a two-dimensional cascade is considered. The method of conformal mapping is used; the two periods of the domain between the blades are mapped onto a rectangle. The solution is expressed in terms of the Jacobian elliptic functions. This is extended to the cases where exists the surface blowing of the fluid due to the distribution of point sources over the blades.
Active flutter suppression (AFS) for a typical two-dimensional airfoil in an incompressible flow is studied in this paper. Root loci with single feedback are first investigated to obtain physical insights into the system described by three aerodynamic modelings. It is shown that the relative location of the three points, which represent section characteristics, plays an important role in the mechanism of aeroelastic instability. Positive and negative feedbacks of the bending displacement or torsion angle can be interpreted to have a virtual effect on reconfigurating these three points. The feedback gains for the AFS system are chosen next by a sequence of truncations from the optimal gains based on the Modal Cost Analysis (MCA). The sequence of truncation, associated cost increases, and closed loop poles are calculated for each truncation. Essential feedback modes and their associated gains for flutter supression can thus be determined efficiently using the MCA.
The plastic deformation and the perforation of thin metallic plates subjected to normal impacts by a spherical projectile are studied. The aluminium plates of 0.3, 0.5 and 0.8mm thick and the copper plates of 0.3mm thick are used for the experiment. Dynamic tangential and normal loads of the plates at the clamping frame are rneasured by small load cells. The peak values of these dynamic loads are found to show the maximum at a little lower velocity than the perforation critical velocity vcr. The values of the perforation energy, the tangential and the normal load of the dynamic perforatiom are compared with the static ones. The dynamic perforation energies are found to be about twice the static ones. The dynamic deflection profiles of the plate are obtained by a still camera and a stroboscope. Both theoretical and experimental deflection profiles show a good agreement.
Anonlinear analysis of the cushion stability of slowly oscillating ACVs has been made. The 'inertance' of the air slug in the ducting has been considered to investigate the unsteady effect. It is found that the unsteady effect becomes noticeable in a frequency range higher than 1 Hz. The result of the analysis is compared with the result of the forced heaving test of a plenum model. The agreement between the two is excellent. It is thus coucluded that the inertance of the air in the ducting is the dominant unsteady effect in a frequency range (up to 1 Hz) of the present study. The effect of compressibility of air in the ducting and the cushion has also been considered quasistatically but it is found to be negligible for the conventional marine ACVs of low cushion pressure and low oscillation frequency.
Aerodyna mic performances are measured for airfoils and circular cylinders with fabric surface. Generally, the critical Reynolds number for the drag of circular cylinder depends on the surface roughness. The measured results of the cylinders with fabric surface agree with the Achenbach's results of sand roughness. The lift to drag ratios of the airfoil(NACA-0012)are much affected by fabric roughness. The differences of the lift to drag ratio between the different roughness are largest near their maximum values and decrease as the angle of attack increases. After the stall no difference appear. The lift to drag ratio is also affected by the directions of stich. The lift to dragratio decreases abruptly as k, the parameter of fabric roughness, increases to 0.2, but over this value its tendency becomes milder.