冲击波垂向加载下PZT 95/5铁电陶瓷的去极化和放电过程分析

电极化后的PZT 95/5铁电陶瓷能够在冲击波作用下快速去极化并释放束缚电荷,形成高功率的瞬态输出电能。对于垂直于极化方向的冲击波加载情况,通过将去极化过程中的铁电陶瓷等效为电流源、电容和电导的并联电路,综合考虑冲击波压力对波速和去极化相变过程的影响,以及冲击波前、后铁电陶瓷的介电常数和电导率变化,建立了描述冲击波垂向加载下PZT 95/5铁电陶瓷去极化和放电过程的模型,解析获得了铁电陶瓷的放电电流表述。在此模型基础上,开展了短路和电阻负载条件下PZT 95/5铁电陶瓷在冲击放电过程中的输出电流特征分析,并与相关实验结果进行了对比。结果表明:模型能较好地模拟实验观测的铁电陶瓷PZT 95/5的冲击放电过程,以及冲击波压力、负载电阻等对冲击放电输出电流的影响规律。     

近场爆炸冲击波对屏蔽压装TNT的冲击引爆试验和仿真

为研究近场强冲击波对屏蔽装药的冲击引爆效应,通过试验和LS-DYNA3D非线性有限元计算程序对屏蔽压装TNT的冲击引爆进行研究,得到了接触爆炸时压装TNT被引爆的临界屏蔽板厚度和非接触爆炸时屏蔽压装TNT的殉爆距离,分析了非接触爆炸时屏蔽板厚度对殉爆距离的影响,并通过非线性最小二乘法拟合得到屏蔽板厚度与殉爆距离的函数关系。结果表明:数值计算结果与试验结果基本一致;接触爆炸时临界起爆的屏蔽板厚度在20～23 mm之间;屏蔽板采用3 mm厚的45钢时,非接触爆炸作用下压装TNT的殉爆距离在12～15 mm之间;非接触爆炸时殉爆距离随着屏蔽板厚度的增加而减小,当无屏蔽板时,压装TNT的殉爆距离为79 mm,当屏蔽板厚度从1 mm加大到9 mm时,殉爆距离从51 mm减为1.5 mm,被发装药的屏蔽板对冲击波有显著的防护作用。     

水下爆炸强冲击波与平板结构相互作用的理论分析方法

针对水下爆炸一维强冲击波与平板结构的瞬态流固问题开展研究,综合考虑流体和结构材料的可压缩性,引入状态方程建立强冲击波在板表面反射后的波阵面参数关系,得到板表面的反射系数。然后依据动量守恒定律建立平板的运动方程,求解得到板表面的壁压及板的速度时程,形成了水下爆炸强冲击波与平板结构相互作用的理论分析方法。在此基础上给出了强冲击波与平板相互作用的冲量传递比近似估算公式。最后开展平板结构的近距及接触水下爆炸实验,并结合数值计算对理论方法进行验证。结果表明,建立的理论方法与实验及数值模拟结果吻合良好,为水下近距爆炸强冲击波与结构的相互作用分析提供了理论基础。     

脉冲电压下的自击穿水介质开关击穿特性和电路参数实验研究

 介绍了“强光一号”加速器中两种结构的自击穿水开关，建立了简化的开关电路模型，并通过估算和Pspice模拟确定了开关的电路参数，包括电极间杂散电容、火花通道电感和火花电阻。研究表明开关导通过程中的流注电容效应可以忽略，放电通道火花电感与电阻选取流注导通时刻的值，且在主放电电流传递过程中保持不变。根据实验结果，阐述了两种开关击穿的不同特点：对于局部电场增强型的球-板电极结构的主开关，可以采用J. C. Martin稍不均匀场水击穿经验公式估算临界场强；而棒-板电极结构的多针开关，适合用J. C. Martin针-板击穿模型的水击穿经验公式估算临界场强，且并联工作的9个多针开关可以同时形成独立的放电通道。     

使用ZFK-500型高速摄影机对液中放电现象的摄影观察

液中放电是通过放电的方式将电能高速转化为热、光、力、声等其他形式的能量。它具有一系列独特的优点,使它广泛应用于许多领域。因此,关于液中放电的研究具有重要的理论与实践意义。我们使用ZFK-500型高速摄影机对液中放电的击穿与弧道过程、冲击波的形成与传播过程,进行了比较成功的观察。大量清晰的摄影,记录了击穿时微弱光线的光导及其在整个放电阶段的情况;记录了液中放电弧道膨胀的特点 此外,不发光现象-冲击波形成与传播过程的记录,都为液中放电的理论研究,提供了十分宝贵的科学依据。     

铝单丝Z箍缩形成无核冕结构的物理分析

针对铝单丝Z箍缩负载,计算其可形成金属蒸气而不形成核冕等离子体的电路和负载参数范围。提出了铝丝电爆炸形成金属蒸气的能量沉积判据和击穿电压判据;建立了热动力学模型,选取电路参数使得金属丝气化时放电回路电流恰好迅速下降,从而避免发生电压击穿。计算了典型电路下的负载电流、电压、电阻及沉积能量的变化曲线,并分析了回路总电感、充电电压以及负载丝长度、直径对其的影响规律。计算结果表明:当储能电容为150pF、充电电压为65kV、回路电感为300nH时,可驱动直径20μm、长2cm的铝丝电爆炸形成铝丝蒸气。快电流前沿、小丝直径和较短的丝长度有助于提高负载中的单位质量沉积能量,容易电爆炸形成金属蒸气负载。     

大水泥岩样的电脉冲压裂实验研究

在20 kV/40 kJ的重复频率压裂系统实验平台上,对大水泥岩样进行了电脉冲水中放电压裂实验。为了模拟井下实际工况,实验时将放电电极装入带有射孔的绝缘套管。水中脉冲放电时岩样中产生定向冲击压力波,冲击波作用于岩层使其产生裂缝。实验结果表明,冲击波通过绝缘套管作用于岩样时有一定的能量损失,部分冲击波压力会施加于绝缘套管,绝缘套管在整个实验期间没有发生形变,电脉冲放电对套管损伤作用极小,重复压裂冲击波会通过射孔在岩样上形成一定规模的微裂缝。去掉绝缘套管后,裸电极作用于岩样造缝效果会更好,裂缝明显的呈现对称规则。     

冲击波加载下孔隙率对Pb_(0.99)(Zr_(0.95)Ti_(0.05))_(0.98)Nb_(0.02)O_3铁电陶瓷去极化性能的影响

制备了四种不同孔隙率的Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3铁电陶瓷,并研究了冲击波作用下孔隙率对陶瓷去极化性能的影响.研究表明:短路负载条件下陶瓷的放电波形不随孔隙的加入而改变,均为方波.多孔陶瓷的放电脉冲幅度较低,脉冲宽度较长.释放的电荷量随着孔隙率的增加而减小,与静态电滞回线测试结果一致.多孔陶瓷具有较低的冲击阻抗,改善了与封装介质的阻抗匹配.用Lysne模型拟合了材料在高电阻负载条件下的放电行为,并指出高电阻负载条件下材料的介电常数是静态介电常数的4—5倍,而且材料的介电常数随孔隙率的增加而减小.冲击波通过样品以后,电路的放电时间常数随着孔隙率的增大而增大.随着电阻的增大,样品负载电压增高,材料铁电-反铁电相变受到抑制,电流上升沿变缓,致密陶瓷出现了击穿现象.     

冲击波压缩PZT-95/5铁电陶瓷的电介质击穿

 应用冲击波加载技术，在垂直加载的条件下，研究了PZT-95/5铁电功能陶瓷的电击穿。通过实验和数值模拟，得到了冲击波加载下的动态击穿特征参数，讨论了其击穿机理。     

静电场中多孔PZT95/5铁电陶瓷的通道电-机械击穿模型及分析

作为爆电电源的多孔PZT95/5铁电陶瓷具有极为重要的工程应用背景,但它在强电场作用下易发生电击穿失效,从而影响其放电效率,甚至造成电源失效。基于多孔PZT95/5铁电陶瓷材料在外电场作用下内部形成导电通道以致电失效的机制,通过通道内部局部放电及通道电-机械击穿机理,建立了导电通道诱导的多孔铁电陶瓷的电击穿模型并进行了相关的理论分析。基于本模型,给出了不同孔隙率下铁电陶瓷的电击穿临界电场强度,预测结果与实验测试结果吻合良好,且材料孔隙率越大,内部电击穿通道的特征尺寸越大,导致铁电陶瓷材料的电击穿临界场强显著降低。     

两个冲击波相互碰撞的演化过程

利用阴影成像诊断技术，对激光约束烧蚀所产生的两个冲击波相互碰撞的演化过程进行了研究.通过分析冲击波相互碰撞在时间上和空间上的演化过程发现，当冲击波相互碰撞的时候，两个冲击波本身并不发生相互作用，而是冲击波与烧蚀等离子体之间发生相互作用.     

Ionizing particles may create shockwaves

To find a model that describes the gas diffusion on irradiated polymers (Makrofol KG polycarbonate) the diffusion constants have been measured with argon as diffusion gas. The polymers were irradiated with uranium, gold and lead ions of about 10 MeV/u and ion fluences between 1×10¹⁰ and 4×10¹¹ ions/cm². The ion irradiated probes show two quite different dependencies of the diffusion constant on the ion energy loss. These effects are strongly related to the fluence of the irradiation. In case of low ion fluences, the diffusion constant is up to 8 times higher than that of pristine material. In the probes with high ion fluences we observe a decrease of diffusion constant to half the value of the pristine material. To understand the dependence of the diffusion constant on ion fluences we apply a model of compacting. This model describes the compacting ability of shockwaves arising from latent tracks. A track formation model is suggested. When an ion penetrates the foil it creates shockwaves around its path. These shockwaves put compacting forces on earlier created latent tracks in the same foil.     

Interaction of short laser pulses with biological structures

Focusing of light pulses emitted by a Q-switched laser, which have a duration of some nanoseconds, into a medium leads to laser-induced breakdown. The shockwaves produced by this propagate through the medium and can interact with inhomogeneities situated within the medium and consequently cause destruction. Because of the increasing interest in these short light pulses in the medical field the interaction of the shockwaves with biological tissue has been investigated. The observed results indicate the influence of two physical quantities of the shockwave: the peak pressure and the duration.     

Sonocrystallization and sonofragmentation

The application of ultrasound to crystallization (i.e., sonocrystallization) can dramatically affect the properties of the crystalline products. Sonocrystallization induces rapid nucleation that generally yields smaller crystals of a more narrow size distribution compared to quiescent crystallizations. The mechanism by which ultrasound induces nucleation remains unclear although reports show the potential contributions of shockwaves and increases in heterogeneous nucleation. In addition, the fragmentation of molecular crystals during ultrasonic irradiation is an emerging aspect of sonocrystallization and nucleation. Decoupling experiments were performed to confirm that interactions between shockwaves and crystals are the main contributors to crystal breakage. In this review, we build upon previous studies and emphasize the effects of ultrasound on the crystallization of organic molecules. Recent work on the applications of sonocrystallized materials in pharmaceutics and materials science are also discussed.     

液电脉冲激波特性分析

基于相应的数学模型来表征液电脉冲激波的产生和传播过程,搭建了液电式碎岩综合试验平台,分析了典型的激波特性的仿真和实测结果。给出了不同充电电压下液电脉冲激波特性的仿真结果,并分析了充电电压对激波特性的影响。结果表明:充电电压为11 kV时,激波的压力峰值为2.67 MPa,激波能量为27.30 J,波前时间为2.16μs,激波加载速率为1.24 MPa/μs,电能转化为激波能量的效率为13.35%;提高电容充电电压,激波压力峰值和激波能量增大,波前时间减少,激波加载速率增加,但电能转化为激波能量的效率降低。利用建模分析的方法,可以根据放电回路参数预测液电脉冲激波特性,从而为进一步研究激波破碎岩石的形态和效果提供理论依据。     

Optical nucleation of bubble clouds in a high pressure spherical resonator

An experimental setup for nucleating clouds of bubbles in a high-pressure spherical resonator is described. Using nanosecond laser pulses and multiple phase gratings, bubble clouds are optically nucleated in an acoustic field. Dynamics of the clouds are captured using a high-speed CCD camera. The images reveal cloud nucleation, growth, and collapse and the resulting emission of radially expanding shockwaves. These shockwaves are reflected at the interior surface of the resonator and then reconverge to the center of the resonator. As the shocks reconverge upon the center of the resonator, they renucleate and grow the bubble cloud. This process is repeated over many acoustic cycles and with each successive shock reconvergence, the bubble cloud becomes more organized and centralized so that subsequent collapses give rise to stronger, better defined shockwaves. After many acoustic cycles individual bubbles cannot be distinguished and the cloud is then referred to as a cluster. Sustainability of the process is ultimately limited by the detuning of the acoustic field inside the resonator. The nucleation parameter space is studied in terms of laser firing phase, laser energy, and acoustic power used.     

An adsorption mechanism underlying phase transformation in stabilized zirconia

Tetragonal-to-monoclinic martensite transformation due to water adsorption was found on the surface of both dispersed and ceramic oxide-stabilized zirconia. The transformation is due to local stretching strains arising in the lattice when the charge state of a stabilizer changes because of water molecules that are chemisorbed on the powder or ceramic surface.     

Porous ceramic membrane with superhydrophobic and superoleophilic surface for reclaiming oil from oily water

A porous ceramic tube with superhydrophobic and superoleophilic surface was fabricated by sol-gel and then surface modification with polyurethane-polydimethysiloxane, and an oil-water separator based on the porous ceramic tube was erected to characterize superhydrophobic and superoleophilic surface's separation efficiency and velocity when being used to reclaim oil from oily water and complex oily water containing clay particle. The separator is fit for reclaiming oil from oily water.     

A method for water well regeneration based on shock waves and ultrasound

The regeneration of water wells is an urgent problem nowadays, when drilling of new wells becomes more and more expensive. Formation damage leads to a reduction of the formation's permeability and/or pore volume which in turn inhibits the ability of the water to flow from the reservoir formation into the wellbore. A new technology that uses high-power ultrasound to remove formation damage of water wells has been developed. The effectiveness of regeneration of wells can be enhanced if ultrasound and shockwaves are used during the same treatment. It was shown by computer modelling, that the two methods have different depths of impact. Whereas the ultrasonic method has a strong impact on the area of the filter tube, the impact of the shock waves is focused on the gavel pack, the wall of the well and the adjacent aquifer. A shockwave treatment, which is normally more effective due to larger impact zone, needs to be followed by ultrasonic treatment in order to facilitate the removal of the detached deposits. These theoretical assumptions were confirmed by field tests on two wells. The use of the method leaded to an increase of the production by 40% and 109% respectively.     

Sono-electrolysis performance based on indirect continuous sonication and membraneless alkaline electrolysis: Experiment,modelling and analysis

In the present study, experiments of membraneless alkaline sono-electrolysis are combined to a mathematical model describing the performance of a sono-electrolyzer based on the electrochemical resistances and overpotentials (activation, Ohmic and concentration) and the oscillation of the acoustic cavitation bubble, and its related sono-physical and sonochemical effects, as a single unit and within population. The study aims to elucidate the mechanism of action of acoustic cavitation when coupled to alkaline electrolysis, using a membraneless H-cell configuration and indirect continuous sonication (40 kHz, 60 W_e). The calorimetric characterization constituted the bridge between experimental results and the numerical and simulation approach, while the quantification of the rate of produced hydrogen both experimentally and numerically highlighted the absence of the contribution of sonochemistry, and explained the role of ultrasounds by the action of shockwaves and microjets. Finally, the energetic sono-physical approach allowed an estimation of the predominance of the shockwaves and microjets effects according to the bubble size distribution within the population corresponding to the acoustic conditions of the study. The resulting macroscopic effect in sono-electrolysis process has been assessed considering the induced degassing. A reduction in the fraction of electrodes’ coverage by bubbles from 76% to 42% has been recorded, corresponding to a decrease of 7.2% in Ohmic resistance and 62.35% in bubble resistance.