冲击加载下孔洞形成微射流的最大侵彻深度

应用二维弹塑性流体力学欧拉程序MEPH,研究冲击载荷作用下孔洞形成的微射流.主要关注孔洞微射流的形成过程,重点分析冲击压力及孔洞半径等因素对于孔洞微射流最大侵彻深度的影响.分析孔洞塌缩形成射流的空间速度分布特征,并应用非定常射流理论,对不同冲击压力及孔洞半径条件下,微射流的最大侵彻深度进行估算,估算结果与数值模拟结果符合较好.     

Kinetics of high-velocity penetration into high-hardness brittle media

A study has been made of the kinetics of penetration of deformable steel and tungsten rods into high-hardness brittle media (ceramics and glass) at impact velocities of 1.3–1.6 km/s. The penetration has been established to occur in two stages. In the first stage, the penetration velocity increases as the ceramic is progressively damaged. The second stage corresponds to quasi-steady-state penetration into a zero-strength medium. It is shown that it is the first stage that determines the high resistance of ceramics to intense impact. The dependence of the resistance to penetration on target geometry and impact pressure has also been established. Fiz. Tverd. Tela (St. Petersburg) 41, 1785–1787 (October 1999) Deceased.     

聚能射流对氧化铝陶瓷靶的侵彻特性研究

 建立了考虑损伤的求解靶板阻力的理论模型,以此来评估陶瓷靶板的抗侵彻能力;数值模拟了长杆弹侵彻氧化铝陶瓷靶的破坏特性,结合实验结果确定了氧化铝陶瓷本构模型中的材料参数。建立了聚能射流侵彻氧化铝陶瓷靶的计算模型,对射流的形成机理及氧化铝陶瓷靶的抗侵彻性能进行研究,讨论了药型罩的几何尺寸对所形成的射流速度及侵彻深度的影响。结果表明：药型罩的锥角和壁厚增大,射流速度减小,壁厚对射流速度梯度的影响较大;同样,药型罩的锥角对侵彻深度也有较大的影响。     

Subcritical penetration of acoustic waves into inhomogenous seafloors

A generalized model is applied to estimate the incoherent penetration ratio caused by volume scattering at grazing angles below the critical grazing angle. The factors that affect volume scattering have been discussed using experimental data in literature. A two-layered model that refers to sound scattering in two-layered media is used to evaluate the incoherent penetration ratio for most typical sediments. But for special cases, such as the experiment, SAX04, a three-layered model is necessary to describe scattering features especially for grazing angles θ<30°. It is shown that subcritical penetration is enhanced when the scale of volume fluctuations is comparable with the acoustic wavelength, and the scattered waves into the seafloor dominate over evanescent waves at depths larger than a few wavelengths.     

Modeling of subcritical penetration into sediments due to interface roughness

Recent experimental results reveal acoustic penetration into sandy sediments at grazing angles below the critical angle. A mechanism for this subcritical penetration is described based on scattering at a rough water-sediment interface. Using perturbation theory, a numerically tractable three-dimensional model is used for simulating experiments. The rough interface scattering has been treated using formally averaged methods as well as with single rough surface realizations. Data-model comparisons show that scattering by interface roughness is a viable hypothesis for the observed subcritical penetration.     

Effect of neoclassical toroidal viscosity on error-field penetration thresholds in tokamak plasmas

A model for field-error penetration is developed that includes nonresonant as well as the usual resonant field-error effects. The nonresonant components cause a neoclassical toroidal viscous torque that keeps the plasma rotating at a rate comparable to the ion diamagnetic frequency. The new theory is used to examine resonant error-field penetration threshold scaling in Ohmic tokamak plasmas. Compared to previous theoretical results, we find the plasma is less susceptible to error-field penetration and locking, by a factor that depends on the nonresonant error-field amplitude.     

聚能装药侵彻混凝土靶板的数值模拟

将MEPH2Y程序和LTZ-2D程序衔接在一起,应用于分析射流、射弹对混凝土靶板的侵彻问题.模拟射流对混凝土靶板的侵彻以及靶板的损伤破坏情况,计算结果与实验结果符合得较好.     

Emergence of a phase transition for the required amount of storage in highly renewable electricity systems

Due to global environmental concerns, our electricity supply will transform from mostly conventional power generation to mostly fluctuating renewable power generation. The transition will require combined backup from conventional sources and storage. A phase transition emerges during the ramp-up of the required amount of storage, with renewable penetration being the control parameter and average relative storage filling level being the order parameter. A singularity appears for the required storage energy capacity at a renewable penetration determined by the parameters of the storage. For an ideal storage with no roundtrip losses the transition occurs at 100% renewable penetration. Moreover, the required storage energy capacity is strongly enhanced by temporal correlations on the synoptic weather time scale. A Markov process is proposed, which reproduces these findings.     

Magnetic flux penetration into high-temperature superconductors in the vortex liquid state under the blow-up conditions

The problem of magnetic field penetration into a type-II high-temperature superconductor that is in the weakly pinned vortex-liquid phase is considered. A magnetic field on the superconductor boundary rises with time in the blow-up regime. A model hydrodynamic equation describing the magnetic induction distribution in the vortex-liquid phase for thermomagnetic motion of the flux is derived. Analytical expressions for the depth and rate of magnetic field penetration into the superconductor are found. It is demonstrated that these quantities depend on parameters of the problem: index of power n in the boundary regime characterizing the penetration rate of vortices into the superconducting half-space and a parameter describing the effect of random pinning forces and thermal fluctuations on the magnetic flux distribution.     

Molecular dynamics simulations of the penetration lengths: application within the fluctuation theory for diffusion coefficients

Mutual diffusion in condensed phases is a theoretically and practically important subject of active research. One of the most rigorous and theoretically advanced approaches to the problem is a recently developed approach based on the concept of penetration lengths (Physica A 320 (2003) 211; Physica A 322 (2004) 151). In the current study, a fast molecular dynamics scheme has been developed to determine the values of the penetration lengths in Lennard–Jones binary systems. Results deduced from computations provide a new insight into the concept of penetration lengths. It is shown for four different binary liquid mixtures of non-polar components that computed penetration lengths, for various temperatures and compositions, are consistent with those deduced from experiments in the framework of the formalism of the fluctuation theory. Moreover, the mutual diffusion coefficients obtained from a coupled fluctuation theory and molecular dynamics scheme exhibit consistent trends and average deviations from experimental data around 10–20%.     

岩石、混凝土和土抗侵彻能力数值计算与分析

利用LS-DYNA3D软件数值计算了弹体侵彻岩石、混凝土和土问题,分析在不同碰撞速度条件下的弹体响应和靶体抗侵彻能力。碰撞速度小于900 m/s时,弹体侵彻岩石的减加速度峰值约是侵彻混凝土的2倍,而侵彻混凝土的减加速度峰值约是侵彻土的6倍。减加速度峰值高则稳态侵彻过程短,弹体能量消耗很快。碰撞速度超过1.5 km/s时,随靶体材料的强度、密度逐渐减小,侵彻深度和孔径逐渐缓慢增加,岩石、混凝土和土3种靶体材料相比,最大侵彻深度增加41%~62%,最大扩孔口径增加16%~25%。     

Measurement of the energy penetration depth into solid targets irradiated by ultrashort laser pulses

The energy penetration depth of a short (100 fs) Ti-sapphire laser pulse (0.8 &mgr;m) of intensity 3x10(16) W/cm(2), in solid density materials has been measured. High-Z (BaF2) and low-Z (MgF2) solid layers targets were used. The penetration depth was determined from the measurement of the x-ray emission spectra, as a function of the target thickness. The investigation of these spectra showed that in the low-Z case, solid density material to a depth of 50 nm was heated to a peak electron temperature of approximately 150 eV. For the high-Z material, the penetration depth corresponding to this temperature exceeded 100 nm. This is evidence of a larger heat penetration depth in a high-Z material in comparison to a low-Z material. A model based on electron heat conduction is used to estimate the energy penetration depth. It is suggested that the larger heat penetration in high-Z material is due to heating of the material, caused by the radiation flux, generated by the electron heat conduction.     

Quantum-mechanical investigation of field-emission mechanism of a micrometer-long single-walled carbon nanotube

A quantum-mechanical simulation is carried out to investigate the charge distribution and electrostatic potential along a 1 microm long (5,5) single-walled carbon nanotube under realistic field-emission experimental conditions. A single layer of carbon atoms is found sufficient to shield most of the electric field except at the tip where strong field penetration occurs. The penetration leads to a nonlinear decrease of potential barrier for emission, which is equally responsible for the low threshold voltage besides the well-known geometrical field enhancement factor.     

Depth range of primary electrons,electron beam broadening,and spatial resolution in electron-beam studies

A comparative analysis of the electron range in solids as a function of the initial electron energy (in the range 1–50 keV) and parameters of matter is performed. A relationship between the full length range of electrons and the depth of their penetration into the target material is established using simple empirical relations. The broadening of an electron beam upon its penetration into a material is considered and the spatial resolution of electron-beam instruments (in particular, in the backscattering mode) is determined.     

The probability of potential barrier penetration in the generalized wkB approximation

The approximation method, discussed in [1], of calculating the coefficients of penetration through one-dimensional potential barriers is unsuitable at small values of the energy. In the present work this insufficiency is removed by applying some additional conditions to the basic potential W(S). A new solution is given for the problem of particle penetration through a symmetric barrier.     

基于速度势侵彻模型的应用研究

 研究了Rubin等人提出的基于Rankine卵形体速度势函数分析的侵彻模型。根据该侵彻模型的基本方法编制了计算程序,计算头部形状为锥形、卵形和球形的长杆弹体垂直碰撞靶板时的侵彻深度和穿透靶板后的剩余速度,分析侵彻模型对不同头部形状的长杆弹体的适用性。另外,利用该分析方法计算并分析了卵形头部长杆弹体对铝靶侵彻和穿透的缩比模型问题,用分析方法验证了无量纲侵彻深度和剩余速度相等的侵彻几何相似规律,同时得到了弹体减加速度与几何尺寸成反比的重要结论。最后对混凝土靶板的侵彻与穿透问题进行了尝试计算,得到了同实验基本一致的计算结果并对其进行了深入分析。     

On the penetration depth of a porous striker moving with a hypersonic velocity

By means of numerical simulation in the framework of the 2D axisymmetric problem of continuum mechanics, the penetration of elongated porous strikers into a steel obstacle under hydrodynamic conditions (the velocity of the striker at collision is several kilometers per second) is studied. It is found that the penetration depth of these strikers exceeds the value predicted from the hydrodynamic theory in the approximation of incompressible fluid. This increase is thought of as being associated with a change in the striker penetration mechanism because of formation of an attached shock. A simple model allowing prediction of the piercing power of elongated porous strikers is suggested.     

三维光滑粒子流体动力学并行计算程序

介绍了基于消息传递并行程序设计平台研制的三维光滑粒子流体动力学并行程序CSPH3D.包括计算格式、并行方案、并行程序逻辑,以及加快邻域粒子搜索的处理方法.对三维微喷射和斜侵彻的计算表明:CSPH3D程序可以较好地计算这类问题.并且程序具有较高的并行效率.对于粒子总数为1527402的微喷射算例和粒子总数为1454225的斜侵彻算例,使用100个处理器时,并行效率可以达到80%.     

Effect of the percentage of normal phase on the penetration of a magnetic field into textured superconducting metallic oxides of yttrium

The penetration of a magnetic field into textured high-temperature superconductors (HTSCs) based on yttrium is studied experimentally. Samples contain impregnations of normal phase (Y-211) in sizes of 1 to 30 micron. A pronounced effect of the percentage of the normal phase on the value of the penetration field is revealed: penetration occurs at lower values of the magnetic field upon a reduction in the percentage of Y₂BaCuO₅. Vortices are shown to penetrate the superconductor in the form of bundles.     

Diffusion along the Grain Boundaries in Crystals with Dislocations

A generalization of the Fisher model of the grain boundary diffusion is suggested, which takes into account the diffusion along short circuit diffusion paths (i.e., dislocations) in the bulk of crystalline grains. For the B-regime of the grain boundary diffusion, three different penetration modes have been found: at the short times the penetration depth of the element diffusing along the grain boundary is given by the Whipple solution of the Fisher model, but with the pipe diffusion coefficients along the dislocation cores instead of the volume diffusivities; at the intermediate times the penetration depth is a weak function of time, and at the large times the penetration depth again increases with time according to the Whipple solution, however, the rate of this increase is much smaller than in the initial period of time. The applications of the model for diffusion in nanomaterials are discussed.