Experimental analysis on hydrodynamic coefficients of an underwater glider with spherical nose for dynamic modeling and motion simulation

In this paper, we present a study of an underwater glider with a cylindrical body, a conical end shape and a spherical nose with NACA0009 airfoil wings. In the experimental section, we investigate the hydrodynamic coefficients of drag and lift as well as the torque on the glider then analyze the launch velocity, launch angles, angular velocity, and displacement range as the main parameters for evaluating of motion dynamics. In the numerical section, we investigate the optimal performance of the glider using the meta-heuristic optimization method in order to find the path and range of motion of the moving mass and control of the sea glider, which is very important for navigation scope. To be specific, body and wings hydrodynamic coefficients are obtained in the velocity range of [0.2, 1] $$m/s$$ m / s ; According to the results, the drag coefficient increases with increasing velocity, while the lift coefficient increases up to velocity of $$0.8 m/s$$ 0.8 m / s , then decreases at velocity of $$1 m/s$$ 1 m / s . Also, the wing drag coefficient decreases with increasing velocity, while the wing lift coefficient increases with increasing velocity. In the next step, in order to calculate an optimum ratio between obtained depth and horizontal distance, the designed algorithm investigate the glider launch angle and finally, the 10 degrees launch angle is chosen as the optimum angle. Subsequently, the analysis performed on mass center displacement range shows that the oscillation interval $$[- 0.045, 0.085]$$ [ - 0.045 , 0.085 ] $$m$$ m is an optimum displacement domain.

Experimental Study of Supercavitation Bubble Development over Bodies in a Duct Flow

Understanding the development and geometry of a supercavitation bubble is essential for the design of supercavitational vehicles as well as for prediction of bubble formation within machinery-related duct flows. The role of the cavitator (nose) of a body within the flow is significant as well. This research studied experimentally supercavitation bubble development and characteristics within a duct flow. Tests were conducted on cylindrical slender bodies (3 mm diameter) within a duct (about 20 mm diameter) at different water flow velocities. A comparison of supercavitation bubbles, developing on bodies with different nose geometries, was made. The comparison referred to the conditions of the bubbles’ creation and collapse, as well as to their shape and development. Various stages of the bubble development were examined for different cavitators (flat, spherical, and conical nose). It was found that the different cavitators produced similar bubble geometries, although at different flow velocities. The bubble appeared at the lowest velocity for the flat nose, then for the spherical nose, and at the highest velocity for the conical cavitator. In addition, a hysteresis phenomenon was observed, showing different bubble development paths for increasing versus decreasing the water flow velocity.

GENERATING PENETRATION RESISTANCE FUNCTIONS WITH A VIRTUAL PENETRATION LABORATORY (VPL): APPLICATIONS TO PROJECTILE PENETRATION AND STRUCTURAL RESPONSE SIMULATIONS

A new software package called the Virtual Penetration Laboratory (VPL) has been developed to automatically generate and optimize penetration resistance functions. We have used this VPL code to generate highly "tuned" penetration resistance functions that can distinctly model the penetration trajectory of steel projectiles into rate-independent, elastic-perfectly plastic aluminum targets. Projectiles with arbitrary nose geometry were considered in this example (i.e. conical, ogival, and spherical nose shapes). The penetration resistance of the aluminum target was determined by numerically solving a series of spherical and cylindrical cavity expansion problems. The solution to these cavity expansion problems were obtained with an explicit, dynamic finite element code that accounts for material and geometric nonlinearities. The resulting cavity expansion equations are then transformed to penetration resistance functions using various transformation algorithms, in order to determine an appropriate method to spatially distribute the resisting stresses on the projectile nose. The resulting penetration resistance functions were then used in a penetration trajectory code to predict the actual trajectories observed from a set of similar experiments.

Penetration of Strain-Hardening Targets With Rigid Spherical-Nose Rods

We developed engineering models that predict forces and penetration depth for long, rigid rods with spherical noses and rate-independent, strain-hardening targets. The spherical cavity expansion approximation simplified the target analysis, so we obtained closed-form penetration equations that showed the geometric and material scales. To verify our models, we conducted terminal-ballistic experiments with three projectile geometries made of maraging steel and 6061-T651 aluminum targets. The models predicted penetration depths that were in good agreement with the data for impact velocities between 0.3 and 1.0 km/s.