Analysis of the Evolution of a Supersonically Expanding Plasma

A supersonically expanding arc plasma in argon is analyzed both experimentally and theoretically. The plasma is created in a cascaded arc and extracted through a hole in the anode. It emanates in a large vacuum system, where it expands supersonically. This expansion is limited by a shock wave. After the shock wave a subsonic plasma beam is created. A quasi one-dimensional model, based on the conservation of mass, momentum and energy is presented. The shock wave is treated as a discontinuity. The electron density, the gas velocity and the gas temperature are measured as a function of the position in the expansion by means of Stark broadening and Doppler spectroscopy. The model calculations agree well with the measurements, especially in the first part of the supersonic flow.     

An experimental switchable stiffness device for shock isolation

The development of an experimental switching stiffness device for shock isolation is presented. The system uses magnetic forces to exert a restoring force, which results in an effective stiffness that is used to isolate a payload. When the magnetic force is turned on and off, a switchable stiffness is obtained. Characterization of the physical properties of the device is presented. They are estimated in terms of the percentage stiffness change and effective damping ratio when switched between two constant stiffness states. Additionally, the setup is used to implement a control strategy to reduce the shock response and minimize residual vibration. The system was found to be very effective for shock isolation. The response is reduced by around 50 percent compared with passive isolation showing good correlation with theoretical predictions, and the effective damping ratio in the system following the shock was increased from about 4.5 percent to 13 percent.     

Multiple tone generation by transonic compressors

An axial flow compressor operating at relative tip speeds in excess of the speed of sound generates a multiple tone acoustic field. A theory is presented which explains this tone field in terms of the production and propagation of the shock waves associated with the supersonic elements of the blading. It is shown how the strengths and positions of these shock waves are sensitive to the small blade-to-blade differences found in practical builds. This causes the complete shock pattern to be unique to each compressor. The propagation of the shock waves along the inlet ducting is analysed. This indicates that whilst the overall strength of the shock system decays, the relative differences between the shock waves are magnified in the propagation process. Ultimately, all similarity of the shock system to its original form is lost, and the steady rotation of the new shock system results in the multiple tone field. The analysis shows how features of the compressor design, as well as the degree of non-uniformity in the blade geometries, can influence the level and character of the radiated field.     

纳秒激光冲击加载的全过程诊断

 与传统的冲击加载方式相比,激光驱动试样具有微尺寸（直径小于1 mm,厚度约10 μm）、超短作用过程（纳秒量级）等特点,但其速度变化历史的实时诊断颇为困难,因此发展适用于激光驱动的高时空分辨率的实时测试技术是十分重要和有价值的。采用桌面式脉冲Nd:YAG激光器作为加载平台,发展了激光加载下的小焦点多普勒光纤探针测量系统（焦斑直径约200 μm,时间分辨力约50 ps）,成功实现了从激光脉冲驱动微尺寸飞片飞行直至撞击Z-切石英试样的全过程实时诊断。实验结果显示,将6 μm 厚Al箔飞片驱动至2.48 km/s时,撞击Z-切石英试样的粒子速度为1.27 km/s,与Hugoniot理论计算结果相符,表明该测试技术是可靠、有效的;多层薄膜靶结构设计（基底/烧蚀层/硅油/Al箔）可提升激光与靶物质的能量耦合效率,使飞片保持更好的宏观完整性。为开展超短脉冲激光加载下材料动态特性研究提供了一种有效的技术途径。     

A Device for Phase Shift Measurement in an Advanced Phase Doppler Velocimeter

Construction and performance of a printed circuit board is described that is built for phase measurement in a state-of-the-art phase Doppler system. Special requirements in treating phase Doppler signals are highlighted and shown to be met satisfactorily by an innovative electronic design that involves signal burst detection, multi-bit sampling, frequency-band narrowing, and phase signal validation based on integrated amplitude and waveform recognition. Performance of the device is measured in terms of phase accuracy for various signal-to-noise ratios, signal frequencies and operating temperatures. The present device is also compared with some alternative techniques for phase measurement.     

Development of extended field Doppler velocimetry for turbomachinery applications

The development of a portable, single component Doppler global velocimetry (DGV) head, based around a wavelength-stabilised argonion laser and a fast digital image-processing system, is described. The normalised two-dimensional DGV image, in which intensities are linearly related to velocities, can be displayed and updated at the 25 Hz camera frame rate, greatly easing the problem of system alignment. The effect of each individual system component upon the velocity resolution achieved for the system as a whole is discussed, and correction factors are calculated to account for the finite aperture and field of view of real systems and for divergence of the illuminating light sheet. Axial velocities of up to 100 m/s in a straight duct flow have been measured, demonstrating an rms velocity resolution of 2.5 m/s. The potential of the technique for gas turbine applications has been demonstrated by measuring the position of a shock in a transonic flow. At a Mach number of 2.3 and mass flow rate of 0.79 kg/s the velocity change across the shock was measured to be approximately 130 m/s.     

40GPa压力范围内铜和铝的准等熵压缩线

 基于自行研制的磁驱动准等熵压缩加载实验装置CQ-1.5,利用全光纤位移干涉仪（Doppler Pins System, DPS）、激光速度干涉计（Velocity Interferometer System for Any Reflectors, VISAR）两种测试手段,以及反积分数据处理方法,实验测量了40 GPa压力范围内T1铜、LY12硬铝和L1纯铝3种材料的准等熵压缩线,将实验准等熵压缩线与基于Grüneisen状态方程的理论等熵压缩线和冲击Hugoniot线进行了比较。结果表明,在该压力范围内,实验准等熵压缩线与理论等熵压缩线相一致,两者偏差小于3%;实验准等熵压缩线靠近冲击Hugoniot线,位于其下方,与国外文献发表的结果相同,进一步表明,实验测量结果正确可靠。     

Exact Shock Measures and Steady-State Selection in a Driven Diffusive System with Two Conserved Densities

We study driven 1d lattice gas models with two types of particles and nearest neighbor hopping. We find the most general case when there is a shock solution with a product measure which has a density-profile of a step function for both densities. The position of the shock performs a biased random walk. We calculate the microscopic hopping rates of the shock. We also construct the hydrodynamic limit of the model and solve the resulting hyperbolic system of conservation laws. In case of open boundaries the selected steady state is given in terms of the boundary densities.     

Planar velocity visualization in high-speed wedge flow using Doppler Picture Velocimetry (DPV) compared with Particle Image Velocimetry (PIV)

A technique for visualizing a velocity field in an entire plane has been developed by taking ‘Doppler Pictures’ using Michelson interferometry. With the Doppler Picture Velocimetry (DPV), information about the instantaneous and local velocities of tracers passing through a light sheet is available. The technique for taking and processing the Doppler pictures has been improved recently and the state-of-the-art of the DPV method will be described with an application in high-speed fluid flows showing the velocity distribution in a light sheet plane crossing a supersonic wedge flow generated in the high-energy shock tunnel STB of ISL. A comparison with Particle Image Velocimetry (PIV) velocity visualizations is also presented.     

Axial flow velocity behind normal ionizing shock waves

The axial flow velocity behind a normal ionizing shock wave propagating in hydrogen has been determined by measuring the Doppler shift of the H_β line emitted by the shock-heated atoms. The value obtained is consistent with the Chapman-Jouguet hypothesis.     

Reversed Doppler effect in photonic crystals

Nonrelativistic reversed Doppler shifts have never been observed in nature and have only been speculated to occur in pathological systems with simultaneously negative effective permittivity and permeability. This Letter presents a different, new physical phenomenon that leads to a nonrelativistic reversed Doppler shift in light. It arises when light is reflected from a moving shock wave propagating through a photonic crystal. In addition to reflection of a single frequency, multiple discrete reflected frequencies or a 10 GHz periodic modulation can also be observed when a single carrier frequency of wavelength 1 microm is incident.     

Shock isolation using an isolator with switchable stiffness

A semi-active control strategy is presented for the shock isolation of resiliently mounted equipment where the isolator has light damping. This is achieved by switching the stiffness of the isolator between a high-state and a low-state. The control strategy involves two stages: the first stage involves the displacement control of the equipment during the shock, and the second stage involves suppression of the subsequent residual vibrations. The performance of the switchable isolation system is illustrated using a base-excited single degree-of-freedom system. It is characterized in terms of the maximum absolute acceleration and displacement of the isolated mass, the relative displacement between the base and the mass, and the effective damping ratio of the system. Provided that the damping in the isolator is light, it is found that the semi-active system can outperform a linear passive system during both stages of control.     

Shock associated noise of inverted-profile coannular jets,part III: Shock structure and noise characteristics

The basic objective of the work described in this paper is to obtain an understanding of the characteristics of shock associated noise from inverted-profile coannular jets in terms of the properties of the shock cell structure and the jet flow. To achieve this, a first-order shock-cell model is developed. Based on the concept that shock-associated noise is generated by the weak interaction between the large-scale turbulent structures in the mixing layers of the jet and the repetitive shock-cell system, formulae for the peak frequencies as well as noise intensity scaling are derived. The calculated results of these formulae agree very favorably with experimental results.     

磁驱动准等熵压缩下单晶氟化锂的光学特性

以"阳"加速器和PTS装置为驱动源,开了展单晶氟化锂(LiF,通光方向[100])窗口材料在准等熵压缩下的光学特性实验研究。应用全光纤激光多普勒探针系统(DPS,激光波长1550nm)同时测量了Ly12铝材料电极加窗和未加窗的后界面速度历史,结合窗口材料修正方法获取了单晶氟化锂窗口材料在实验条件下折射率随密度的变化和界面粒子速度修正因子。每次实验可获取窗口材料样品的连续加载历史数据,进而处理得到LiF窗口材料在近50GPa准等熵压力范围内的修正因子。结合拟合的线性关系,进一步处理获得了在实验过程中折射率随密度的变化。将这些实验结果与D.E.Fratanduono,Y.Ma,B.J.Jensen的对应数据比较,其中与光子多普勒测速系统(PDV,1550nm)测量结果基本相符,不确定度与多次冲击实验得到的结果相当。     

Theoretical study of the microscopic Doppler effect for energetic material

We develop a physical model to describe the microscopic Doppler effect of phonon states in energetic material and use it to investigate the phonon–strain scattering behaviour of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine. The required elastic constants and force constants are obtained by first-principles calculations. By using the phonon–strain scattering probability, a set of dissipation parameters are calculated, such as the viscosity coefficient, damping rate of elastic wave, and heat dissipation across shock wave front. It is interesting that the Doppler effect could describe the microscopic phonon scattering mechanism reasonably.     

超声动态向量血流成像的产品化实现

传统超声彩色多普勒成像测量的是血流沿超声传播方向上的速度分量,故无法得到垂直于超声传播方向的血流。向量血流成像是一种更加先进的超声血流成像技术。它不受角度限制,可以直接计算出血流速度的大小和方向。本文总结了现有多种超声向量血流成像技术的特点和发展情况,并从产品化实现的角度分析了各项技术的优缺点。从超声系统发射接收、血流成像、向量速度方向合成、显示等几个方面详述了迈瑞超声向量血流成像技术产品化实现过程中遇到的主要问题及解决方案。实验采用了中科院声学所研制的超声多普勒仿血流体模,通过向量血流成像和脉冲多普勒成像分别测量体模的仿血流速度。将向量血流成像直接计算出来的速度值与脉冲多普勒经过角度校正得到的速度进行对比。在不同条件下,经过多次测量,二者的平均相对误差均在10%以内。     

Structural instability in fluid-structure systems under hydrodynamic shock conditions

The effects of non-linear fluid-structure interaction on the dynamic buckling of structures are investigated. In particular the structural buckling characteristics are studied for the case of a strong shock wave propagating through a fluid medium striking a structure. Non-linear terms are retained for both fluid and structural systems. A one-dimensional example consisting of a perfect gas-spring-mass system is solved for shock wave loading. Solutions are obtained by using the finite element method. The numerical methods utilized appear to be applicable to complex multi-dimensional systems. It is shown that in a non-linear fluid-structure interaction problem the incident pressure may be amplified significantly during reflection from a structure. Thus, an acoustic fluid model may be non-conservative for strong shock problems. Structures in a fluid will buckle at an incident pressure level which is much less than that which causes buckling in a vacuum.     

Nonlinear Dispersive and Dissipative Electrostatic Structures in Two-Dimensional Electron-Positron-Ion Quantum Plasma

The nonlinear features of two-dimensional ion acoustic(IA) solitary and shock structures in a dissipative electron-positron-ion(EPI) quantum plasma are investigated. The dissipation in the system is taken into account by incorporating the kinematic viscosity of ions in plasmas. A quantum hydrodynamic(QHD) model is used to describe the quantum plasma system. The propagation of small but finite amplitude solitons and shocks is governed by the Kadomtsev-Petviashvili-Burger(KPB) equation. It is observed that depending on the values of plasma parameters(viz.quantum diffraction, positron concentration, viscosity), both compressive and rarefactive solitons and shocks are found to exist. Furthermore, the energy of the soliton is computed and possible solutions of the KPB equation are presented numerically in terms of the monotonic and oscillatory shock profiles     

平面冲击下铜的拉伸应变率相关特性研究

本文对冲击加载下高纯无氧铜的拉伸应变率相关特性进行了实验研究.实验中利用磁测速系统测试撞击前飞片速度,利用光纤位移仪——多普勒探针系统测试样品自由面粒子速度剖面.对自由面速度剖面的特征参量进行计算分析,结果表明:铜样品的层裂强度随着拉伸应变率的增加而增加,对比发现层裂强度不仅受加载条件的影响,同时受到材料本身微细观结构影响;同时随着拉伸应变率的增加,自由面速度的回跳斜率呈现出先缓慢增加后迅速增加的临界特性;最后,通过层裂样品中波系相互作用,给出了自由面速度回跳过程中的振荡特征随着拉伸应变率增加而逐渐消失的物理过程.     

多普勒效应教学仿真系统的开发

Visual Basic 2010 Express Edition(VB2010)软件开发环境下利用OpenAI和OpenGL API函数库设计并实现多普勒应用教学仿真系统,经过优化的该系统仅需两个扬声器就能实现3D位置音效及多普勒效应.应用表明,多普勒效应教学仿真系统具有交互性好、实用性强和效果逼真等特点.