The paper studies the forces occurring during motion of the underwater cavity projectile. This paper also investigates the effect of the length of projectile and the mass distribution of the projectile to the magnitude of impact force and the drag force of the underwater cavity projectile. | Journal of Science and Technology 54 (6) (2016) 797-807 DOI: STUDY ON IMPACT FORCES OF THE UNDERWATER CAVITY PROJECTILE Nguyen Thai Dung1, *, Nguyen Duc Thuyen1 Military Technical Academy, 236 Hoang Quoc Viet, Hanoi * Email: thaidung1966@ Received: 2 October 2015; Accepted for publication: 26 October 2016 ABSTRACT The motion of the underwater projectile with cavity effect includes two motions: First, the projectile moves in the forward direction. Second, the projectile’s center of mass rotates about its tip. Because of this rotation, its tail impacts on the cavity wall. Accordingly, the impact forces occur, they include the drag force at its tip and the impact force at the impact point. The paper studies the forces occurring during motion of the underwater cavity projectile. This paper also investigates the effect of the length of projectile and the mass distribution of the projectile to the magnitude of impact force and the drag force of the underwater cavity projectile. Keywords: cavity, number cavitation, wetted length, underwater cavity projectile. 1. INTRODUCTION A cavity can be maintained by one of the two ways: (1) achieving such a high speed that the water vaporizes near the tip of the body; (2) supplying gas to the cavity at nearly ambient first technique is known as vaporous or natural cavity. The second is termed ventilation or artificial cavitation [1].The underwater projectile moves with high - speed, the local pressure at its tip will decrease. Until this local pressure is less than or equal to the vapor pressure, the bubbles appear from its tip and they surround a part of projectile. If the velocity of projectile is more than 50 m/s, a field of bubble covers over the projectile. This phenomenon is called the underwater cavity projectile (Figure 1a). During the motion of projectile, only its nose contacts water. This explains why the drag force reduces greatly. After a certain time, because of .
