Jet Formation in Plasma Sprayers

Optospectroscopic studies of plasma jets in powder sprayers have been made. It has been shown that the jet of the PlasmaTechnik AG sprayer is a periodically pulsating formation similar to that generated by the twojet plasma torch. A scheme of a plasmasonic reactor for treatment and synthesis of gaseous and condensed materials is proposed.     

Jet configuration in accompanying flows

A method is described for integrating on a MN-7 analog computer the energy equations relevant to a moving medium with heat sources, for the two-dimensional adiabatic problem, allowing for compressibility. Jet temperature and velocity fields for accompanying flows in the combustion of methane, obtained by machine integration, are presented.     

Numerical investigations in penetration mechanics

Computational techniques have been employed to investigate a variety of phenomena associated with the penetration process including cratering in thick targets and the perforation of thin targets. The dependency of these phenomena on impact velocity, material properties and projectile-target configurations are investigated for a variety of impact situations. Comparisons of the computational results with experimental data are made for those cases for which such data are available; agreement between theory and experiment is quite good.     

聚能射流侵彻混凝土靶射孔形状变化趋势分析

使用二维欧拉程序AUTODYN-2D,采用多流体网格法对锥型罩聚能装药产生的金属射流侵彻混凝土靶板的过程进行数值模拟,重点分析射流侵彻过程中,射孔尺寸随时间变化的趋势和规律,并与试验结果进行比较,得出一些规律性的结论,弥补了试验研究中不能实时跟踪测量射孔尺寸变化的局限性。     

Plasma Jet Machining

Plasma Jet Machining (PJM) is a surface figuring technology based on atmospheric plasma assisted chemical etching or deposition, respectively. In both cases a sub‐aperture plasma jet source is used combined with a CNC multi‐axes system for the processing of curved surfaces. It is under development for the surface figuring of a variety of optical materials by IOM for about 15 years. PJM is capable to figure deep aspheric or free‐form substrates with high material removal rate and high spatial resolution. Based on chemical reactions between plasma generated radicals and the surface PJM does not introduce any damage to the processed surface and sub‐surface region in contrast to abrasive techniques. Deterministic deposition of SiO_x layers and subsequent proportional transfer using ion beams or polishing is another plasma jet based technique for surface figuring that extends the range of machinable materials. The article gives an overview on the current state of PJM development in IOM and shows examples of its application.     

Phase three penetration

Phase three penetration is defined as the target penetration that occurs after a high-velocity penetrator has fully eroded. Phase 3 penetration is due to one or the combination of after-flow and secondary penetration of the target by the eroded penetrator debris. Recent experimental data for long tungsten rods penetrating confined boron carbide, aluminum nitride, and silicon carbide targets are used to investigate phase 3 penetration. It is found for these three ceramic targets that the onset impact velocity for the occurrence of phase 3 penetration is very roughly 2 km/s. The phase 3 penetration increases with impact velocity approximately as v². For these experiments the phase 3 penetration appears to be due almost entirely to secondary penetration.     

Ice penetration tests

Exploratory tests of ice penetration were made by driving small blunt cylinders into semi-infinite ice at normal incidence. Three types of laboratory tests were made: (1) drop-weight impact (impact speed 1.4–3.1 m/s), (2) high-speed ballistic penetration (impact speed 83–434 m/s), (3) deep penetration at low speed (0.42–4.23 m/s). Penetration by indenters and projectiles could be characterized by the energetics of the process, with little variation of specific energy as penetration speed changed by orders of magnitude. For blunt penetrators entering ice at ?5°C, specific energy was typically in the range 1.5–15 MJ/m³. Low speed tests provided data on penetration force (and energy) as a function of displacement. The test results were compared with other published laboratory data, and with field test results for bigger projectiles.     

Superdeep penetration efficiency

The efficiency of an explosive accelerator is analyzed. The efficiency of the stream of particles in penetrating into a target to ultralarge depths is determined. Pis’ma Zh. Tekh. Fiz. 24, 81–84 (September 12, 1998)     

Monte Carlo calculation and experimental verification of the photon energy response of tooth enamel in a head-sized plexiglas phantom

The use of electron paramagnetic resonance (EPR) tooth dosimetry for calculation of organ doses requires conversion of the measured absorbed dose in enamel. Before deriving conversion factors from simulation calculations with a realistic anthropomorphic human phantom, in the current study a simplified phantom was chosen to compare EPR measurement and Monte Carlo calculation. The dose response of tooth enamel of molars at various positions inside a cylindrical Plexiglas phantom of head-size was calculated hy Monte Carlo modelling in parallel photon beams of X rays of 63 keV equivalent energy and 60Co gamma rays (1.25 Mev). For X ray exposure, preliminary results of EPR dosimetry with tooth enamel samples prepared from molars irradiated in the phantom were in agreement with calculation. The mean value of the ratio of the measured to the calculated dose was 0.93 +/- 0.08.     

Jet flow in a porous layer

The problem of fluid (gas) flow originating during jet injection in a cylindrical apparatus filled with a porous layer of finite height is solved. Pressure and velocity distributions in the layer are obtained. The influence of the walls of the pipe containing a granular layer on the velocity profile of a one-dimensional filtration layer is investigated.     

Bubbly Jet Impingement in Different Liquids

The impingement of bubbly jets in distilled water and ethanol has been experimentally studied on ground. An experimental apparatus for the study of jet impingement on ground and in microgravity has been designed. The opposed-jet configuration with changeable orientation is used in order to study which is the better disposition to achieve an efficient mixing process. The impact angle between jets that can be changed from 0° (frontal collision) up to 90° (perpendicular collision). The impinging jets are introduced into a test tank full of liquid by means of two bubble injectors. The bubble generation method, insensitive to gravity level for low Bond numbers, is based on the creation of a slug flow inside a T-junction of capillary tubes of 0.7 mm of diameter. Bubble velocities at the injector outlet and generation frequencies can be controlled by changing gas and liquid flow rates. Individual bubble properties and coalescence events, as well as the whole jet structure are analyzed from the images recorded by a high speed camera. Bubble velocities are compared with the velocity field of a single-phase jet. Rate of coalescence between bubbles is found higher in ethanol than in water, creating a higher dispersion in bubble sizes.     

Enhancement of Particle Removal Performance of High-speed Air Jet by Setting Obstacle in Jet Flow

Surface cleaning using high-speed air jet can be applied to cleaning of an object with concavo-convex shape. In such cases, the distance between the air jet nozzle and the surface becomes on the order of cm. An increase in the distance causes a decrease of the air velocity at the surface resulting in deterioration of the particle removal performance of the air jet. Therefore, a method to enhance removal efficiency is required. In this study, we investigated two methods for the enhancement of removal efficiency: one is to set a wire in the air flow and the other is to set two cylindrical rods. Although the wire set at the center of the jet flow deteriorates the removal efficiency, experimental results imply that the wire has a positive effect on the efficiency when it is set at a position where it does not interfere with the main flow of the jet. On the other hand, when two cylindrical rods are set at a theoretical periphery of the air jet, it shows clearly an enhancement in removal efficiency. This fact implies that the removal efficiency can be enhanced by controlling flow fluctuation by means of setting an obstacle.     

Condensation Wake in a Nonisobaric Jet

We demonstrate the substantial effect of the nonisobaricity of an exhaust jet on the initial parameters of a condensation wake: distance to the wake, initial water content, ice content, optical thickness, and transverse dimension.     

Simulation of hypervelocity penetration in limestone

A parameter study was performed to examine the (shock) damage obtained with long-rod and spherical mono-material penetrators impacting two varieties of limestone. In all cases, the impacts were assumed to be normal to the plane of the rock and at zero angle of attack (in the case of the rods). Impact velocities ranged to 15 km/s but most calculations were performed at 4 and 6 km/s and the penetrator mass was fixed at 1000 kg. For unlined underground structures, incipient damage was defined to occur when the peak stress, σ_pk, exceeds 1 kb (100 MPa) and the applied impulse per unit area, I_pk, exceeds 1 ktap (1 kb μs). Severe damage was assumed to occur when σ_pk exceeds 1 kb and I_pk exceeds 1000 ktaps. Using the latter definition it was found that severe damage in hard, non-porous limestone with spherical impactors extended to a depth of 9 m on-axis for an impact velocity of 4 km/s and 12 m at 6 km/s. Cylinders with length-to-diameter (L/D) ratio of 8.75 achieved depth to severe damage of 23 and 40 m, respectively, under the same conditions. For a limestone medium with 2% initial gas porosity, the latter numbers were reduced to 12 and 18 m.     

Material similarities in long-rod penetration mechanics

The process of long-rod penetration into thick metallic targets is examined through a series of two-dimensional simulations. The aim of the research presented here is to uncover the inherent material similarities in this process. In particular, the search is for non-dimensional parameters which account for the depth of penetration, such as the density ratio, and the relative strengths of penetrator and target. The simulation results are in accord with existing empirical data, shedding more light on the penetration process and emphasizing the difficulties in achieving an overall normalization procedure for this process.     

Moisture penetration patterns in thin films

A technique is described for examining moisture adsorption in narrow band filters; it involves the photographing of the filter in monochromatic light and the analysis of the patterns obtained. The mechanism of moisture penetration and its influence on filter drift is discussed. Changes in the structure of the layers due to heat treatment can be detected by change in the moisture penetration patterns.     

Chloride penetration into concrete in marine environment-Part II: Prediction of long term chloride penetration

The development of chloride penetration models is essential for the assessment of the service life of concrete structures exposed to marine environment. Simple models derived from Fick's second law of diffusion are at present the best way to predict the chloride penetration in practical situations. However these models need to be calibrated with experimental results. This paper presents an experimental study where the parameters used in the penetration model were calibrated to allow the prediction of long term chloride content in concrete. The results showed that both the concrete cover and concrete quality requirements stated in the present codes need to be increased so that an acceptable service life can be achieved.     

Hypervelocity penetration of ceramics

The penetration resistance of alumina was found to decrease with velocity for armor-piercing bullets. However, it was relatively independent of velocity for rods and fragment-simulating projectiles. These results are explained in terms of compressive yielding caused by high velocity pointed projectiles.