Publications on underwater drag reduction by gas have been gathered in the present study. Experimental methods, results and conclusions from the publications have been discussed and analyzed. The stable existence of gas is a requirement for underwater drag reduction induced by slippage at the water-solid interface. A superhydrophobic surface can entrap gas in surface structures at the water-solid interface. However, many experimental results have exhibited that the entrapped gas can disappear, and the drag gradually increases until the loss of drag reduction with immersion time and underwater flow. Although some other surface structures were also experimented to hold the entrapped gas, from the analysis of thermodynamics and mechanics, it is difficult to prohibit the removal of entrapped gas in underwater surface structures. Therefore, it is essential to replenish a new gas supply for continued presence of gas at the interface for continued underwater drag reduction. Active gas supplement is an effective method for underwater drag reduction, however, that needs some specific equipment and additional energy to generate gas, which limits its practical application. Cavitation or supercavitation is a method for passive gas generation, but it is only adaptive to certain vehicles with high speed. Lately, even at low speed, the evaporation induced by liquid-gas-solid interface of a transverse microgrooved surface for continued gas supply has been discovered, which should be a promising method for practical application of underwater drag reduction by gas.

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Underwater drag reduction by gas

Friction and wear between rotating band and gun barrel during engraving process

The soft deformable metallic rotating band of large caliber projectiles prevents the gas leakage between the gun tube wall and the shell body by the band pressure on contact surfaces during the launch cycle of the gun. High rotating band pressures can lead to problems concerning gun tube wear, fatigue, and strength. The effects of changes in construction of rotating band and long range artillery projectile shell body on gun tube loading are studied experimentally. A practical analysis method for tube inner wall pressure computation from outer wall strain measurements is presented. The method is based on assuming stepped pressure load affecting on tube inner wall surface, when the projectile passes the measurement point. Although the analysis method was simplified, it was found to give useful and reliable results for comparative verification of different shell and band structures and their influences on gun tube loading. The structural design of the shell body and the rotating band were shown to be the most important aspects to cause the extreme loadings on the gun tube.

Influence of Rotating Band Construction on Gun Tube Loading: Part II: Measurement and Analysis

Transient finite element for in-bore analysis of 9mm pistols

The engraving process of a projectile rotating band is one of the most basic research aspects in interior ballistics, which has not been thoroughly understood thus far. An understanding of this process is of great importance from the viewpoints of optimal design, manufacturing, use, and maintenance of gun and projectile. In this paper, the interaction of copper and nylon rotating bands with a CrNiMo gun barrel during engraving was studied under quasi-static and dynamic loading conditions. The quasi-static engraving tests were performed on a CSS-88500 electronic universal testing machine (EUTM) and a special gas-gun-based test rig was designed for dynamic impact engraving of the rotating bands. The mechanical behaviors of copper and nylon were investigated under strain rates of 10−3 s−1 and 2 × 103 s−1 using an MTS 810 and a split Hopkinson pressure bar (SHPB), respectively. Morphologies of the worn surfaces and cross-sectional microstructures were observed with scanning electron microscope (SEM) and optical microscope (OM). It was found that large deformation and severe friction occur during engraving. The surface layer is condensed and correlated with a hardness gradient along the depth from the top worn surface. The structure of the rotating band and gun bore, band material, and loading rate have great effects on band engraving. The flow stress-strain of the copper strongly depends on the applied strain rate. It is suggested that strain rate and temperature play significant roles in the deformation mechanism of rotating bands.

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Tribology of rotating band and gun barrel during engraving process under quasi-static and dynamic loading

The effects of changes in geometries and material properties of rotating band and long range artillery projectile shell body on gun tube stress are presented. The results are based on numerical calculations (finite element analysis, FEA). Numerical explicit dynamic analyses were performed assuming elastic–plastic material behavior and nonlinear kinematics. Mechanical loading of shell body was controlled by pressure–time relationship based on the simulation of internal ballistic cycle. One degree slice of projectile and forcing cone section of gun tube was modeled as simplified smooth bore 3D analysis model. The results were in agreement with the measured results in firing trials and also with the results presented in open literature. Although simplified computations were used, the influences of the structural modifications of the rotating band and the shell body were shown.

Janne Tervokoski

Papers

Influence of Rotating Band Construction on Gun Tube Loading—Part I: Numerical Approach

Influence of Rotating Band Construction on Gun Tube Loading: Part II: Measurement and Analysis