Numerical analysis of homogeneous condensation in rarefaction wave in a shock tube by the space-time CESE method

A detailed numerical investigation has been carried out for the homogeneous condensation of water vapor in a non-stationary rarefaction wave generated in a shock tube. The space-time CESE method has been adopted to simulate the mutual interaction of condensation with the rarefaction wave for an extremely long time. It is found that the homogeneous condensation in the rarefaction wave has a significant influence on the flow due to the latent heat release and the continuous change of cooling rate. Three stages can be defined in this process: the initial stage which contains the onset of the condensation and the formation of the condensation shock waves in both downstream and upstream directions, the oscillating stage which is characterized as the repeat of quench and onset of condensation in the expansion fan approximately in a logarithm time manner, and the asymptotic stage which the oscillating waves are damping out with time and no apparent condensation shock wave is formed.     

A lightweight sensing method of tooth-touch sound for disabled person using remote controller

To support disabled people to use remote controllers, several biological signals are used. The tooth-touch is one of desirable biological signals. This is because it is the simple and natural human behavior. However, a sophisticated signal processing to extract only the tooth-touch sound is needed since the tooth-touch sound is mixed with the voice sound. This paper proposes a lightweight sensing method extracting the tooth-touch without a sophisticated signal processing to eliminate only voice sound from the sound wave in which tooth-touch and voice are mixed. Instead of the audible sound wave, proposal uses a shock wave (i.e., ultrasonic wave) which is generated when the upper tooth and the lower tooth hit each other. Using the shock wave generated to detect the tooth-touch, a trivial high-pass filter can eliminate only voice sound in the lower frequency domain than in the ultrasonic domain including the tooth-touch. Through a preliminary experiment that uses a conventional microphone and well-known digital high-pass filter, we show that the used electret microphone can sense the tooth-touch as ultrasonic wave and the high-pass filter can extract only tooth-touch. Then, we show some robustness of our method by using the sound waves including the voice and tooth-touch. In addition, we design the filtering hardware to implement a small and cheap system-on-chip achieving a real-time operation. Through the implementation of Field Programmable Gate Array, and the simulation, we show that our hardware is small and performs well for a real-time operation.     

超声波在干细胞治疗中的应用进展

超声波是指频率在 20 kHz 以上的机械波,具有机械效应、热效应和空化效应。不同强度的超声波作用于生物体,会对其器官、组织和细胞等产生不同程度的生物学效应。随着工程技术的发展,超声波已在医学显像、实体肿瘤治疗等生物医学领域具有广泛应用,低强度超声波也成为辅助干细胞治疗各类疾病的重要工程手段。深入了解超声波在干细胞治疗中所起的作用及机制,将促进广大研究者对超声波技术的了解,从而重视并加大超声波在该领域的研究力度及广泛应用。该文综述了超声波在干细胞治疗中的研究进展,对超声促进干细胞增殖、分化和迁移、细胞示踪显影及靶向药物传递等前沿研究进展进行了全面介绍,并对超声波在干细胞治疗领域的应用前景提出了设想。     

Lagrangian simulation of oil droplets transport due to regular waves

Dispersed oils (i.e., oil droplets) at sea are transported by convection due to waves and buoyancy and by turbulent diffusion. This work follows the common approach in the oil community of using a Lagrangian approach instead of the Eulerian approach. Our focus was on small scale simulation of oil plumes subjected to regular waves. Stokes' theory was used to obtain analytical expressions for wave kinematics. The velocity above the Mean Water Level was obtained using a second order Taylor's expansion of the velocity at the MWL. Five hundred droplets were used to simulate the plume for a duration of 60 wave periods. A Monte Carlo framework (300 simulations) was used to compute theoretical mean and variance of plumes. In addition, we introduced a novel dimensionless formulation, whose main advantage was to allow one to report distances in terms of the wave length and times in terms of the wave period. We found that the Stokes' drift was the major mechanism for horizontal transport. We also found that lighter oils propagate faster but spread less than heavier oils. Increasing turbulent diffusion caused the plume to disperse deeper in the water column and to propagate less forward. The spreading in both vertical and horizontal directions increased with an increase in turbulent diffusion. The increase in wave slope (or wave steepness) caused, in general, an increase in the downward and horizontal transport. In the context of mixing in the water column, the dimensionless formulation showed that small steepness waves with a large turbulent diffusion coefficient could result in essentially the same spreading as large steepness waves with a small turbulent diffusion coefficient.     

Real-time target tracking applied to improve fragmentation of renal stones in extra-corporeal lithotripsy

In extra-corporeal shock wave lithotripsy (ESWL), focused acoustic waves are used to fragment urinary stones. The success of the treatment depends on coincidence between the stone position and the point of convergence of the waves. However, the stone may move during the treatment. We developed a software called Echotrack which performs a real-time tracking of the stone in ultrasound images and automatically adjusts the position of the generator of shock waves. Clinical tests carried out in 65 patients showed that the Echotrack is able to track the stones as long as they are visible in the images. The number of shocks necessary to fragment the stones is reduced by 40%. Received: 28 April 1998 / Accepted: 10 September 1998     

电磁超声体波方法对内部孔洞缺陷检测研究

电磁超声是一种新型的超声检测方法,其具有非接触、不受工作环境影响、易于激发多种类型的超声波等优点。本文研究了电磁超声体波对结构件内部孔洞缺陷探测问题,首先利用离散点源实现对电磁超声声场的分析;而后利用有限元方法对电磁－结构多场耦合建模,研究超声体波在体内缺陷处的波型转换以及模式转换后爬波在缺陷表面传播情况;最后利用电磁超声体波对孔洞缺陷的尺寸、位置进行了定量检测。有限元计算结果与简化解析求解得到较好的验证,本文为电磁超声对体内孔洞缺陷的应用评估提供良好基础。     

基于维纳滤波的超声增强实现方法

超声在传播时,由于受到材质不均匀、材料内部杂质等的影响而使接收信号受到噪声的干扰,这种干扰有时会淹没所检测的裂纹信号,因此必须要经过增强处理。声学增强处理常用的方法是维纳滤波。本文提出维纳滤波用于超声增强的具体实现方法,即首先统计平均无脉冲段的初始噪声功率谱,然后自适应计算带干扰超声段功率谱,最后进行维纳滤波。超声数据在不同信噪比下的维纳滤波实验表明了所提方法的有效性,超声维纳去噪方法与谱减法一样能够降低超声回波中的噪声,且更加有效。     

涡激振动行波动力学特征的数值模拟

采用数值模拟分析了水中大长径比结构物涡激振动行波动力学特征,以及水动力学阻尼和模型初始张力对于行波动力学特征的影响.数值模拟模型采用改进的尾流振子模型,该模型考虑了涡激振动横向运动和顺流向运动之间的耦合,考虑了张力沿模型长度的变化和流体的耗散.给出了用于评估行波在整个振动波中所占比例的方法,该方法采用行波椭圆来定量表征行波所占的比例,即行波比.数值模拟结果显示,行波比总体上呈现随流速增加的趋势,但在模态阶数变化的临界流速上突然降低.水动力学阻尼显著影响着行波比,阻尼比越大,行波比越大,行波对于整个振动波的贡献就越大.不同张力情况下,行波比突然下降的临界速度不同.初始张力影响模型的固有频率,影响模态阶数发生转变的流速,从而影响了行波比突然下降的临界流速.     

Simulations of bifurcation processes of reflected-shock waves in ionizing argon in a shock tube

A finite-difference procedure, which numerically solves the thin-layer Navier-Stokes equations with ionization reactions, has been developed to predict ionizing nonequilibrium flows generated by strong shock waves. By using the procedure, simulations were carried out for bifurcated reflected-shock waves in ionizing argon in a shock tube. Results are shown for the reflection process of an ionizing shock moving at Mach No. 14 in argon at 400 Pa and 298 K. Computed flowfields are compared with snap-shot shadowgraphs for reflected-shock waves in ionizing argon. Qualitative agreement between the simulations and the experiments is excellent.     

基于宽波束激励的高帧频超声成像方法研究

超声成像的帧频是影响超声成像应用的一个关键因素,成像系统的帧频决定了系统捕捉运动组织的能力,如3D成像、心脏成像、彩色多普勒等。传统超声成像采用延迟聚焦方法可获得较好的图像,但成像帧频较低。目前提高超声成像帧频主要有平面波成像和宽波束激励成像两种方法。平面波成像是通过激励所有阵元同时发射并同时接收超声波,虽在帧频上获得了显著提高,但由于它使用非聚焦技术,分辨率的提高仍然比较有限,特别是当要维持较高帧率而使用较少的扫描角度时,得到的图像质量仍然不高。宽波束成像技术利用多阵元同时发射超声波、远点聚焦、动态实现孔径变迹等方法可极大地提高图像的帧频、均匀性和空间分辨率。文章通过美国 Verasonics公司 V-1数据采集系统采集宽波束数据,进行波束合成建立宽波束超声图像,并与平面波成像和传统聚焦成像技术进行了对比和分析。实验结果表明,相较于平面波成像和传统聚焦成像方法,宽波束成像具有更好的横向分辨率和轴向分辨率,且可获得比传统聚焦方法更高的帧频。     

A new shock/discontinuity detector

A new effective shock/discontinuity detector has been developed in this work. The detector has two steps. The first step is to check the ratio of the truncation errors on the coarse and fine grids, and the second step is to check the local ratio of the left- and right-hand slopes. The currently popular shock/discontinuity detectors such as Harten's, Jameson's and WENO can detect shock, but mistake high-frequency waves and critical points as shock and then damp the physically important high-frequency waves. Preliminary results show that the new shock/discontinuity detector is very delicate and can detect all shocks including strong, weak and oblique shocks or discontinuity in function and first-, second- and third-order derivatives without artificial case-related constants, but never mistake high-frequency waves and critical points or expansion waves as shock. This will overcome the bottleneck problem with numerical simulation for the shock–boundary layer interaction, shock–acoustic interaction, image process, porous media flow, multiple phase flow, detonation wave, and anywhere the high-frequency waves are important, but discontinuity exists and is mixed with high-frequency waves. After detecting the shock, we can then use one-side high-order scheme for shocks and high-order central compact scheme for the smooth parts if the shock is appropriately located. Then a high-order universal subroutine for the finite difference method is developed, which can be used for any finite difference code for accurate numerical derivatives.     

一种用于测量弹丸激波的传感器

介绍了激波传感器的研制过程。该传感器采用杯式膜片结构的压电转换原理,解决了许多传感器性能指标的矛盾关系,提高了灵敏度,在能承受较大平衡压力的基础上又能分辨微弱压力的变化,适合于超音速飞行弹丸产生的激波的压力测量。     

Acoustophoresis of hollow and core-shell particles in two-dimensional resonance modes

Motivated by the applications of ultrasonic particle manipulation in a biotechnological context, a study on acoustophoresis of hollow and core-shell particles is presented with analytical derivations, numerical simulations and confirming experiments. For a long-wavelength calculation of the acoustic radiation forces, the Gor’kov potential of hollow, air-filled particles and particles with solid or fluid core and shell is derived. The validity as well as the applicable range of the long-wavelength calculation is evaluated with numerical simulations in Comsol Multiphysics^®. The results are experimentally verified in the acoustic field of an intrinsically two-dimensional fluid resonance mode, which allows for a more complex analysis than the common one-dimensional ultrasonic standing waves or their superposition to two-dimensional fields. Experiments were conducted with hollow glass particles (13.9 μm diameter) in a microfluidic chamber of 1.2 mm × 1.2 mm × 0.2 mm on a silicon-based device with piezoelectric excitation around 870 kHz. The described resonance mode is of additional interest for particle trapping and medium exchange on certain particle types, and it reveals a novel approach for particle characterization or separation.     

Selective particle and cell clustering at air–liquid interfaces within ultrasonic microfluidic systems

In this study, we demonstrate particle and cell clustering in distinct patterns on the free surface of microfluidic volumes. Employing ultrasonic actuation, submersed microparticles are forced to two principal positions: nodal lines (pressure minima) of a standing wave within the liquid bulk, and distinct locations on the air–liquid interface (free surface); the latter of which has not been previously demonstrated using ultrasonic standing waves. As such, we unravel the fundamental mechanisms behind such patterns, showing that the contribution of fluid particle velocity variations on the free surface (acoustic radiation force) results in patterned particle clustering. In addition, by varying the size and density of the microparticles (3.5–31 μm polystyrene and 1–5 μm silica), acoustic streaming is found to increase the tendency for a smaller and lighter particle to cluster at the air–liquid interface. This selectivity is exploited for the isolation of multiple microparticle and cell types on the free surface from their nodally aligned counterparts. Free surface clustering is demonstrated in both an open microfluidic chamber and a sessile droplet, as well as using a range of biological species Escherichia coli, blood cells, Ragweed pollen and Paper Mulberry pollen). The ability to selectively cluster submersed microparticles and cells in distinct patterns on the free surface showcases the excellent suitability of this method to lab-on-a-chip systems.     

Molecular dynamics simulations of diffusion of submonolayer polar liquid lubricant films on solid surfaces

A fundamental understanding of the diffusion phenomena of submonolayer polar liquid films is important for achieving reliable lubrication between moving mechanical parts separated by a nanometer-sized gap. To acquire this understanding, we conducted molecular dynamics (MD) simulations of diffusion phenomena of submonolayer polar perfluoropolyether (PFPE) Zdol films on solid surfaces. To improve the accuracy of these simulations, we developed an all-atom model that includes hydrogen-bond potential and refined atomic charges for Zdol molecules and tested it through MD simulations of spreading of step-shaped submonolayer PFPE films. Our MD simulations reproduced the experimentally observed effects of polar end groups on the diffusion speed and molecular conformation of Zdol. We then conducted MD simulations of self-diffusion of submonolayer Zdol films; these simulations demonstrated that as the thickness of the submonolayer Zdol films decreases, molecular conformation becomes flatter and the self-diffusion coefficient decreases. These changes in molecular conformation partially explain our experimental finding that the spreading of step-shaped submonolayer polar PFPE films slows down with decreasing initial thickness.     

Formulation of Kinetic Energy Preserving Conservative Schemes for Gas Dynamics and Direct Numerical Simulation of One-Dimensional Viscous Compressible Flow in a Shock Tube Using Entropy and Kinetic Energy Preserving Schemes

This paper follows up on the author’s recent paper “The Construction of Discretely Conservative Finite Volume Schemes that also Globally Conserve Energy or Enthalpy”. In the case of the gas dynamics equations the previous formulation leads to an entropy preserving (EP) scheme. It is shown in the present paper that it is also possible to construct the flux of a conservative finite volume scheme to produce a kinetic energy preserving (KEP) scheme which exactly satisfies the global conservation law for kinetic energy. A proof is presented for three dimensional discretization on arbitrary grids. Both the EP and KEP schemes have been applied to the direct numerical simulation of one-dimensional viscous flow in a shock tube. The computations verify that both schemes can be used to simulate flows with shock waves and contact discontinuities without the introduction of any artificial diffusion. The KEP scheme performed better in the tests.     

基于微控制器的钻杆扭矩测量及其超声-蓝牙分级无线传输系统

为实时测量狭窄金属钻杆钻头的扭矩信息,基于微控制器设计了钻杆底部的扭矩数据采集终端,实现扭矩信号数字化并将数据OOK调制于超声波,利用超声波实现钻杆内的数据无线传输,解决了钻杆内电磁波衰减严重的问题。在钻杆顶部设置数据接收终端,接收超声信号并通过蓝牙链路将数据无线发送至上位机。上位PC机通过蓝牙适配器无线接收超声信号并解调恢复扭矩数据。这种联合超声-蓝牙的分级无线技术为狭窄金属屏蔽管内的无线数据传输提供了一种新的思路。     

Influence of numerical and viscous dissipation on shock wave reflections in supersonic steady flows

Numerical simulations are investigated to describe precisely the shock wave reflections in supersonic steady air flow field. The main objectives are to study the influence of the wedge trailing edge corner angle, of the numerical methods and of the viscous effects on the shock wave reflections and on the hysteresis behavior. The computations are done with different MUSCL-TVD finite volume schemes and the corresponding results are compared. The flow viscosity is also taken into account and comparisons are made between inviscid and viscous flow simulations. The results display the non-negligible influence of the numerical scheme accuracy on the results, mainly on the position and height of the Mach stem, and the relatively weak influence of the flow viscosity on these parameters. Comparisons between numerical results and experimental data have also been done and a good agreement is only observed for small wedge angles mainly due to the three-dimensional effects in the experimental setup.     

Simulation of biological waves in single-species bacillus system governed by birth and death-diffusion dynamical equation

Based on both the theories of cellar biology and the results of experimental observations a dynamical model of birth and death-diffusion type has been suggested for popular growth of bacillus and evolution of nutrition in the single-species bacillus system with a growth–propagation source. It has been verified that the single-species bacillus system in the process of growth–propagation has the biological wave behaviors from the experimental observation. Furthermore, under a special initial values and boundary conditions corresponding to the point-source growth in a closed culture-container, the evolutionary equations of this dynamical model in the single-species bacillus system with a growth–propagation source and the combination of biological waves in the single-species bacillus system with two growth–propagation sources are analyzed by means of the computer simulation, respectively. It shows that the popular growth of single-species bacillus systems governed by birth and death-diffusion dynamical equation is characterized by the spatial-temporal quasi-periodicities which is consistent with the traveling wave solution of above evolutionary equations. It turns out that these results of computer simulation, we obtain could qualitatively copy and describe the phenomenon from experimental observations. The results reported in this paper are a powerful support to the famous argument of the biological wave about the popular growth of bacteria based on lab-observation in ecology.     

Safety-monitoring-type wide-range detectable contact sensor system using ultrasonic waves and viscoelastic tubing

In physical human–robot interaction, a contact sensor is fundamentally required for robots to sense contact with humans and to take appropriate safety measures. This paper proposes a wide-range detectable contact sensor system with a safety monitoring function that uses an ultrasonic wave and a silicone rubber tube. The appropriate threshold voltage for generating a monitoring pulse signal is calculated using the estimation equation derived on the basis of the propagation characteristics of ultrasonic waves in straight and curved tubes. By comparing the periodic time between the generated monitoring signals and self-diagnostic signals, the proposed contact detection algorithm detects both contact due to tube deformation and failure of a sensor system including a stack fault. An experiment investigating the relationship between tube deformation by pushing force and the loss of peak voltage of an ultrasonic wave reveals that the sensor system can detect contact when the tube is deformed by 8 mm.