ИСТИНА

The two-dimensional problem of thin body motion in uid parallel to the boundary at a distance comparable with the length of the body was regarded. The uid was assumed occupying in nite semispace, gravity was neglected as compared with uid inertia. The solution was obtained for a problem of plate motion in compressible uid at a de nite depth under free surface, constant velocity and inclination angle. The formation of nal length cavity behind the body was taken into account. Vapor pressure in the cavity is assumed to be less than the pressure on free surface. The solution allows determining drag and lift forces. The relation between the body length and the cavity length in the case of small depth or high compressibility was obtained. It was determined that the forces increase when the pressure in the cavity decreases. When the pressure in the cavity tends to the pressure on the free surface the length of the cavity in nitely increases and forces tend to the values obtained in independent solutions with in nite cavities. The increase of depth under free surface and decrease of compressibility brings to decrease of cavity length.