Numerical Investigations of Cavitation Nose Structure of a High-Speed Projectile Impact on Water-Entry Characteristics

In this study, a detailed analysis of the influences of cavitation nose structure of a high-speed projectile on the trajectory stability during the water-entry process was investigated numerically. The Zwart-Gerber-Belamri (Z-G-B) cavitation model and the Shear Stress Ttransport (SST)k-ω turbulence model based on the Reynolds Averaged Navier–Stokes (RANS) method were employed. The numerical methodology was validated by comparing the numerical simulation results with the experimental photograph of cavitation shape and the experimental underwater velocity. Based on the numerical methodology, the disk and the conical cavitation noses were selected to investigate the water-entry characteristics. The influences of cavitation nose angle and cavitation nose diameter of the projectile on the trajectory stability and flow characteristics were carried out in detail. The variation features of projectile trajectory, velocity attenuation and drag were conducted, respectively. In addition, the cavitation characteristics of water-entry is presented and analyzed. Results show that the trajectory stability can be improved by increasing the cavitation nose angle, but the drag reduction performance will be reduced simultaneously. Additionally, due to the weakening of drag reduction performance, the lower velocity of the projectile will cause the damage of the cavitation shape and the trajectory instability. Furthermore, the conical cavitation nose has preferable trajectory stability and drag reduction performance than the disk cavitation nose.

Experimental study on water entry of cylindrical projectiles with different nose shapes

Water entry experiments of projectiles with different nose shapes were performed under different entry angles and velocities using high-speed photography technology. The cavity flow characteristics of the near water surface, including splash jet, splash crown, surface seal of cavity, pull away, deep seal of cavity and cavity collapses, were systematically investigated using a high-speed camera. The emphasis of the study is paid on the effect of nose shape, water entry angle and velocity on the evolution of the air entraining cavity. The experimental results demonstrate that the nose shape of projectile has a significant influence on the jet flow, the cavity diameter and trajectory stability in the case of certain other conditions. On the other hand, the splash scale, cavity diameter increase gradually with the increasing of the water entry velocity, as well as the cavitation closed in advance. Furthermore, the water entry angle of the projectile plays an important role in the cavity evolution and the close type.

Analytical studies of the technological parameters of the curved channel of the pneumatic separator

Purpose. Establishment of the laws governing the movement of particles in the air flow with an uneven distribution of flow velocity and the action of additional forces arising from this. Methods. Theoretical studies are based on the basic principles of theoretical mechanics, in particular dynamics, as well as the theory of differential equations of the first and second order Results. A mathematical description is obtained of the movement of particles of the grain mixture in the chamber of a gravity-air separator during the action of air flows of variable speed, as well as the trajectory of particles with different sizes. With certain assumptions, the obtained patterns of change in the velocity of a material particle (point) from coordinates. Conclusions 1.Based on theoretical studies, taking into account deflecting forces, the possibility of separating particles of grain material into fractions by aerodynamic properties in vertical channels and with a lower discharge is determined. 2.The use of air flow as a separating carrier can significantly increase the value of the splitting of the trajectories and the criterion for the separation of grain into fractions. 3.Created simplified mathematical models of the movement of the components of the grain material in air separators with vertical channels, which allow us to determine the rational modes of operation of new technical means. Keywords: air flow, variable air speed, trajectory, stability of forces, fractions, fractionation process, grain mixture, air separator, pneumatic circular flow.

Effect of Pressure-Equalizing Film on Hydrodynamic Characteristics and Trajectory Stability of an Underwater Vehicle With Injection Through One or Two Rows of Venting Holes

Pressure-equalizing film is a slice of air film generated through exhausting and attached to the vehicle's exterior with nearly uniform inner pressure. Similar to ventilated cavity in composition, but of interest, here is the weakening of pitching moment and environment disturbance that the film offers, the film's forming speed and covering range upon vehicle determine the improvement effect of vehicle's trajectory stability as it emerges from water. This paper established a numerical approach to investigate the effect of single and double rows of venting holes on the evaluation of air film along vehicle's exterior, at the same time its influence on the trajectory stability of vehicle with three degrees-of-freedom (3DOF) motion is also analyzed. Results indicate that reverse flow forms between row-to-row spacing when exhausting with two rows of holes, which enhances the exhausting process with the film's size enlarged and axial length extended, meanwhile it brings about more complex vortices structure near venting holes compared to the single-row hole case. As for the 3DOF cases, the pressure difference between vehicle's front and back sides is dramatically reduced attributing to the existence of attached air film, consequently the rotation of vehicle is weaken, leaving a better attitude to vehicle after it piercing water surface. Besides, the rapid formation of air film in double-row hole cases is advantage for the timely inhibiting of vehicle's pitching motion compared to the single-row hole cases, and their weaker stagnation high pressure near film's closure region is also good for the reduction of vehicle's lateral load.

Processing of Cells’ Trajectories Data for Blood Flow Simulation Model*

Simulations of the red blood cells (RBCs) flow as a movement of elastic objects in a fluid, are developed to optimize microfluidic devices used for a blood sample analysis for diagnostic purposes in the medicine. Tracking cell behaviour during simulation helps to improve the model and adjust its parameters. For the optimization of the microfluidic devices, it is also necessary to analyse cell trajectories as well as likelihood and frequency of their occurrence in a particular device area, especially in the parts, where they can affect circulating tumour cells capture. In this article, we propose and verify several ways of processing and analysing the typology and trajectory stability in simulations with single or with a large number of red blood cells (RBCs) in devices with different topologies containing cylindrical obstacles.

Trajectory Stability in the Traveling Salesman Problem

Two generalizations of the traveling salesman problem in which sites change their position in time are presented. The way the rank of different trajectory lengths changes in time is studied using the rank diversity. We analyze the statistical properties of rank distributions and rank dynamics and give evidence that the shortest and longest trajectories are more predictable and robust to change, that is, more stable.