Mechanism of EDM Intensification at Ultrasound Application

This paper considers some theoretical provisions on the impact ultrasonic mechanical vibrations have on the throughput of an electroerosive piercing of small-diameter holes. The approximate estimates confirm the hypothesis that the cumulative jets mechanism makes the greatest contribution to the intensification of a multiphase medium flow in the interelectrode gap. A model is proposed for a periodic localization of the cavitation region in the bottom part of the annular side gap. It allows explaining the occurrence of a multiphase medium flow during hole processing.

Some aspects of the shaped-charge perforator certification and qualification problem

The problem of certification of shaped-charge perforators appear to be very important in oil and gas production. The paper considers five aspects of the problem. First, it is a physical aspect, which means the problem is viewed from the point of view of the physics of a cumulative explosion; the second aspect is a methodological one, which implies the most desirable, permissible, unacceptable methods of certification and qualification; the next aspect is economic, it focuses on the economy on a large scale, allowing a possible loss in a small one. Perhaps, there are things that are currently more important than the most correct physical considerations and the most perfect methods, so technical and political aspects arise. The final aspect is an organizational one which implies a rational division of powers of government departments. The most important and science-intensive aspect is the physical one, as it is associated with the design, construction, and operation of shaped charges of perforators, and this is the main focus of the paper. The paper carefully analyzes the formation, movement in free space, and action on the combined obstacle: steel — concrete — rock of monolithic and powder cumulative jets from metal and composite materials. Moreover, the study comparatively assesses the penetrating action of shaped charges of perforators according to various methods, both domestic and foreign, and assesses economic, technical, political, and organizational factors in the development of the shaped charges certification procedure. Finally, the study gives recommendations for carrying out certification and qualification tests of shaped charges of perforators in Russia.

State of the art in cavitation erosion studies

Object and purpose of research. This paper discusses cavitation erosion on propeller blades. The purpose of this work is to review and analyse modern studies on cavitation erosion, as well as to apply these research results for better under-standing of cavitation damage risk on full-scale propellers. Materials and methods. The paper reviews recent studies on cavitation erosion, as well as the author’s own findings in cavitation erosion on full-scale steel propellers, analyzing the energy needed to create cavitation damage of recorded size. This energy was calculated as per the model based on the results of metallurgical studies discussing the effect of shot blasting upon steel properties. Comparison of these results with those obtained as per classic formulae for the collapse energy of cavita-tion bubble made it possible to estimate the conditions of cavitation erosion on propeller blades. Main results. The review of recent studies on cavitation erosion has shown that current progress in the technologies of experimental studies and computer-based simulations made it possible to considerably improve the knowledge about cavitation erosion process as compared to the level of the 20th century. This review shows that cavitation erosion studies followed three practically independent paths: experimental studies and computer-based simulation of flow around propeller blades with locali-zation of peaks for one or several criteria reflecting the intensity of cavitation energy fluctuations; the studies intended to esti-mate the pressure exerted by collapsing cavitation bubbles and emerging cumulative jets; and finally, the studies on the proper-ties of materials affected by cumulative jets and collapsing bubbles. At this point, it would be practicable to merge these three paths using the results of full-scale cavitation erosion analysis for propellers. KSRC findings in cavitation damage of full-scale steel propeller has shown that cavitation damage recorded in these studies might occur due to a certain combination between the required energy, bubble-blade interaction pressure and the size of affect-ed area on steel blade surface, and this combination, in its turn, might take place when cavitation bubbles consisting of vapour fraction with partial air content hit the blade surface and collapse. Conclusion. This paper shows the capabilities of modern research methods in obtaining new data on the inception mecha-nism of cavitation erosion. Still, to develop the methods for prediction of cavitation erosion (in particular, on propellers), it is necessary to merge the results obtained in different branches of cavitation studies. The basis for this merging could become a power-based analysis of cavitation processes, with help of the cavitation erosion model suggested in this paper and based on the similarity between cavitation erosion and shot-blasting.

SHAPED CHARGES WITH THIN AND ULTRA-THIN FACINGS

The aim of the research is to study the formation of cumulative jets in charges with cumulative facings with a wall thickness of the order of the thickness of the jet-forming layer in classical charges. Based on mathematical modeling and experiments, it is shown that in such charges, the detonation products of explosives can play the role of an additional body that affects the axial velocity of the lin-ing throwing and leads to a collapse angle of more than 180 degrees. In this process, the mass of the jet is greater than the mass of the pestle. For the first time, corrugations were experimentally detected on the surface of the lining during its explosive compression. Corrugations may occur on the surface of the lining, leading to instability of the cumulative jet formation process. As a result of the study, it was found that the minimum wall thickness of the cladding is mainly determined by the instability of its surface (the appearance of corrugations on its surface).

Interaction of an accelerating layer with a cloud: formation of tails and cumulative jets

ABSTRACT We consider the penetration of spherical dense cloud into a planar layer of gas that is in gravitational equilibrium in a constant field of gravity with acceleration W. We take into account the compressibility of the medium in contrast to the classical problem of a drop falling on the surface of an incompressible fluid. Our goal is to study the formation of cumulative jets in relation to the conditions on the borders of H ii regions. We determine those features of motion that would distinguish jet streams from inhomogeneities of a different origin. Our simulation has shown that cumulative jets may arise in the presence of an acceleration layer W. The gas in jet moves in the direction opposite to the initial velocity Vc. At the same time, there are both a cumulative jet and tails, teardrop-shaped condensations, caused, respectively, by gas inflow in the wake behind the cloud and the classical Rayleigh–Taylor instability. We assume the model, according to which the H ii RCW 82 region formed in an initially homogeneous cloud. In framework of this model, we estimated the characteristic time of a cumulative jet formation ts ≈ 0.15 Myr. This is less than the present age of the H ii RCW 82 region, which is about 0.4 Myr. From the obtained estimates, it follows that the conditions at the periphery of the H ii RCW 82 region are favourable for the manifestation of cumulative effects on scales of ∼1.4 × 1017 cm, which are significantly smaller than the layer thickness.

The new model of erosion destroying

A new physical (experimental) model of cavitation destruction of the studied materials is proposed. In the mo-dern model of the cavitation effect, the destruction of materials is associated with the impacts of cumulative jets, which are formed during the asymmetric slamming of cavitation bubbles near the solid surface and the shock waves that occur during their compression. In the new model, erosion damage is explained by the formation of cavitation tubes (с-tubes) with a spiral high-frequency structure in the materials under study that were previously unknown in the literature. The destruction of materials is associated with the focusing of acoustic energy along the axis of the spiral structures. When focusing energy, there is a significant increase in pressure and temperature along the axis of the spiral structures, which leads to the destruction of the materials under study.