A comparison study of multi-component Lattice Boltzmann models for flow in porous media applications

A comparison study of three different multi-component Lattice Boltzmann models is carried out to explore their capability of describing binary immiscible fluid systems. The Shan–Chen pseudo potential model, the Oxford free energy model and the colour gradient model are investigated using the multi-relaxation time scheme (MRT) algorithm to study the flow of binary immiscible fluids. We investigate Poiseuille flow of layered immiscible binary fluids and capillary fingering phenomena and evaluate the results against analytical solutions. In addition, we examine the capability of the various models to simulate fluids with significant viscosity and density contrast and suitable interface thickness. This is of great importance for large scale flow in porous media applications, where it is important to minimise the interfacial thickness from a computational point of view. We find that the Shan–Chen model can simulate high density ratios up to 800 for binary fluids with the same viscosity. Imposing a viscosity contrast will lead to highly diffusive interfaces in the Shan–Chen model and therefore this will affect significantly the numerical stability. The Free Energy model and the colour gradient model have similar capabilities on this point: they can simulate binary fluids having the same density but with significant viscosity contrast. This is of great importance to study the flow of water, supercritical CO₂ and oil in porous media, for CO₂ storage and Enhanced Oil Recovery (EOR) operations.     

Integrated microfluidic viscometer equipped with fluid temperature controller for measurement of viscosity in complex fluids

In the study described herein, a microfluidic viscometer equipped with fluid temperature controller is proposed for measuring the viscosity of complex liquids containing cells or particles. The microfluidic viscometer is composed of a microfluidic device and a fluid temperature controller. The microfluidic device has two inlets, for the introduction of the sample and reference fluids, respectively, and a spacious diverging channel with a large number of identical indicating channels. A fluid temperature controller, which contained a Peltier chip, micro thermocouples, and a feedback controller, is applied for the consistent control of the temperature of the fluids in the microfluidic channels. For accurately identifying fluid viscosity, an effective design criterion is discussed using an enhanced mathematical model for complex fluid networks. The accuracy of the proposed model is sufficiently investigated via numerical simulations as well as experimental measurements. As performance demonstrations, pure liquids [five different concentrations of SDS (Sodium Dodecyl Sulphate)] and complex fluids (four different blood samples) were used to evaluate the performance of the proposed microfluidic viscometer. This investigation indicated that the proposed microfluidic viscometer is capable of accurately and simply measuring both Newtonian and non-Newtonian fluids, even without the need for calibration procedures, and artifacts faced with a conventional viscometer. We therefore conclude that our proposed microfluidic viscometer has considerable potential for the precise and easy measurement of complex fluid viscosity.     

Multiplexed microfluidic viscometer for high-throughput complex fluid rheology

We report the first multiplexed microfluidic viscometer capable of measuring simultaneously the viscosity as a function of shear rate for multiple samples. The viscometer is based on a flow-comparator technique where the interface location between co-flowing streams of test and reference fluids is a sensitive function of the viscosity mismatch between the two fluids. We initially design a single microfluidic viscometer and study two different modes of comparator operation—the interface displacement (ID) mode and the interface compensation mode (IC). We find that both modes yield viscosity curves for Newtonian and polymeric fluids that are consistent with a conventional rheometer. Based on the results from the single microfluidic viscometer, we present an operating window that serves as a guide to assess accessible viscosities and shear rates. We then design a 4-plex and 8-plex viscometer based on the ID mode and show that it is capable of reliably measuring viscosity curves for Newtonian fluids, polymeric solutions and consumer products. Collectively, our results demonstrate that the multiplexed viscometer is capable of measuring in a parallel format, viscosities of fluids spanning nearly three orders of magnitude (≈10^?3–1 Pa s) across a shear rate range of ≈1–1,000 s^?1. We believe our multiplexed viscometer is a low cost and high-throughput alternative to conventional rheometers that analyze samples serially using expensive robotic liquid-handling systems. The multiplexed viscometer could be useful for rapidly analyzing a wide selection of complex fluids on-site during product formulation and quality control.     

A micromechanical flow sensor for microfluidic applications

We fabricated a microfluidic flow meter and measured its response to fluid flow in a microfluidic channel. The flow meter consisted of a micromechanical plate, coupled to a laser deflection system to measure the deflection of the plate during fluid flow. The 100 /spl mu/m square plate was clamped on three sides and elevated 3 /spl mu/m above the bottom surface of the channel. The response of the flow meter was measured for flow rates, ranging from 2.1 to 41.7 /spl mu/L/min. Several fluids, with dynamic viscosities ranging from 0.8 to 4.5/spl times/10/sup -3/ N/m, were flowed through the channels. Flow was established in the microfluidic channel by means of a syringe pump, and the angular deflection of the plate monitored. The response of the plate to flow of a fluid with a viscosity of 4.5/spl times/10/sup -3/ N/m was linear for all flow rates, while the plate responded linearly to flow rates less than 4.2 /spl mu/L/min of solutions with lower dynamic viscosities. The sensitivity of the deflection of the plate to fluid flow was 12.5/spl plusmn/0.2 /spl mu/rad/(/spl mu/L/min), for a fluid with a viscosity of 4.5/spl times/10/sup -3/ N/m. The encapsulated plate provided local flow information along the length of a microfluidic channel.     

基于小型爆燃发生装置的温度传感器动态特性标定

针对现有基于激波管及热风洞的温度传感器动态特性标定方法存在装置体积大、成本高、阶跃幅度小或边沿斜率低等缺点,提出了一种以自反应物质热分解瞬间释放大量气体为基础,通过压力膜片破裂产生高速爆燃气流的温度传感器动态特性标定方法,建立了标定过程非稳态传热模型,分析了影响标定结果的重要因素,设计了相应的小型化标定装置.仿真结果显示,该方法所获时间常数与气流流速呈负相关,与阶跃温度幅度呈正相关关系;实验结果表明,该方法可以实现几十毫秒级时间常数温度传感器动态特性标定,对应用于高压、强对流的温度传感器动态特性标定及选型具有较高的实用价值.     

Dynamic and kinematic viscosity measurements with a resonating microtube

This paper examines the use of a micromachined resonating tube to measure both the dynamic viscosity and density of a fluid enabling the calculation of the kinematic viscosity. Dynamic viscosity is measured using the damping effect that a fluid has on the motion of the resonating tube. Fluid damping requires a change in drive voltage to maintain a constant vibrational amplitude. The density is measured via the change in resonant frequency caused by a change in fluid density while the viscosity is measured by monitoring the peak signal of the resonator. The dynamic viscosity measurement error between the new sensor and the calibration references ranges from 0.006 to 0.15 cP, or 0.6 to 8%. A variety of applications for the sensor will be discussed.     

Calibration procedure for piezoelectric MEMS resonators to determine simultaneously density and viscosity of liquids

Microsystem Technologies - The main objective of this work is the assessment of a calibration method for piezoelectric MEMS resonators for simultaneous density and viscosity sensing. A device...     

基于功率谱密度的结构随机疲劳寿命仿真

利用MSC．Patran、MSC．Nastran、MSC．Fatigue软件,通过对某设备的弹簧片结构进行强度和疲劳寿命分析,详细地探讨随机振动疲劳仿真分析技术的流程及实现过程：即首先对结构进行频率响应计算,得到弹簧片的传递函数,再将此传递函数与输入的功率谱相乘．获得弹簧片的应力功率谱密度,再结合材料参数,选择合适的疲劳损伤模型,利用频域方法计算结构的疲劳寿命。通过对真实结构进行的随机疲劳试验证明仿真所得结果与试验结果处于同一量级,仿真的结果真实可靠。     

Coupling of rigid body dynamics and moving particle semi-implicit method for simulating isothermal multi-phase fluid interactions

The moving particle semi-implicit (MPS) method does not require grids for simulating fluid motions. Therefore, the MPS method can easily handle a large deformation of fluid. However, the MPS method has some difficulties in simulating transfer of momentum caused by a physical collision between different fluids because fluid particles have no mass or volume and only have weights for interacting with other particles. To overcome this inherent defect of the MPS method, rigid body dynamics is explicitly coupled with the MPS method in this study. In the first step, the MPS calculation is performed with particles which are considered to have no mass or volume. In the second step, rigid body dynamics comes into the calculation and considers the particles to have a slightly lesser diameter than the initial distance between particles. Then, physical contacts between particles are simulated with the dynamic energy conserved while the incompressibility of fluids is effectively maintained. In the single fluid region, the coupled method deals with the behavior of the particles. For the interface of the different fluids, only rigid body dynamics is used to simulate the transfer of the momentum caused by physical collisions of fluids. Through this coupling of rigid body dynamics and the MPS method, the overall stability related with the incompressibility of a fluid is comparatively increased in the single-phase fluid simulation. For the calculation of the multi-phase fluids behavior, fluids interactions can be easily treated with improving stability of the MPS calculation. In this study, collapse of water column and the isothermal fuel–coolant interaction (FCI), in which a water jet is directed into a denser fluid pool, were simulated to validate the coupling method of the MPS method and rigid body dynamics.     

Statistical micromechanical method for dynamic kinetic binary interaction among moderate dense gene-regulating bio-molecules

A statistical thermodynamical approach has been introduced to calculate shear viscosity and thermal flux for interactions among the gene-regulating biomolecular protein particles that operate in moderate density rigid-sphere fluids. Starting from the modified Boltzmann equation with the help of linear perturbation theory, the coefficients of distribution function were determined. On the basis of transport theory, we introduced computational forms of diffusion constant, mass flux, shear viscosity, and thermal flux. We examined the influences of changes in mass, diameter, and magnitude of the pair correlation function. The present method will be available to evaluate the local physical reaction properties of the gene-regulating particles.This work was presented, in part, at the 8th International Symposium on Artificial Life and Robotics, Oita, Japan, January 24–26, 2003     

多投影面沉浸式虚拟环境系统的颜色校正

提出一种颜色校正的函数逼近优化模型来解决多投影面沉浸式虚拟环境系统的颜色校正问题。该颜色校正模型，采用数码相机作为颜色反馈的测量仪器，获得一个基准投影面的亮度和色度转换函数；为其他投影面分别寻找一个亮度修正函数和色度修正函数，使得各投影面与基准投影面的亮度和色度转换函数之间的L2距离最小，进而根据各修正函数来补偿各投影机的输入响应差别以达到它们之间的颜色一致。给出了逼近校正方法的算法及其程序实现，通过一个三通道的试验系统，证明了此方法对解决多投影面沉浸式虚拟环境系统颜色校正问题的有效性。     

A Hybrid Approach to Multiple Fluid Simulation using Volume Fractions

This paper presents a hybrid approach to multiple fluid simulation that can handle miscible and immiscible fluids, simultaneously. We combine distance functions and volume fractions to capture not only the discontinuous interface between immiscible fluids but also the smooth transition between miscible fluids. Our approach consists of four steps: velocity field computation, volume fraction advection, miscible fluid diffusion, and visualization. By providing a combining scheme between volume fractions and level set functions, we are able to take advantages of both representation schemes of fluids. From the system point of view, our work is the first approach to Eulerian grid‐based multiple fluid simulation including both miscible and immiscible fluids. From the technical point of view, our approach addresses the issues arising from variable density and viscosity together with material diffusion. We show that the effectiveness of our approach to handle multiple miscible and immiscible fluids through experiments.     

结合小波消噪的捷联惯导系统传递对准性能改进

针对机载捷联惯导系统的传递对准问题,给出了一种速度+姿态匹配算法,旨在强调姿态失准角和惯导器件误差参数估计性能的改善.并基于惯导测量单元 (inertial measurement unit,IMU)原始测量信号的频谱特征,引入了小波串级消噪算法,拟通过对IMU测量进行消噪,进一步提高传递对准的性能.仿真结果验证了所提算法的可行性.     

Numerical analysis of non Newtonian fluid flow in a low voltage cascade electroosmotic micropump

In microfluidic devices, many fluids have non-Newtonian behaviors, especially biofluids. The viscosity of these fluids mostly depends on the shear rate. Sometimes the non-Newtonian fluids should be transferred by micropumps in lab-on-chip devices. Previous researchers investigated the flow rate in simple electroosmotic flow micropumps which have a simple channel geometry. In the present study, the effects of non-Newtonian properties of fluid in a low voltage cascade electroosmotic micropump are numerically investigated using the power law model. The micropump is modeled in two dimensional with one symmetric step and has a more complex geometry than previous studies. The numerical results show that, the non-Newtonian behavior of fluid affects flow rate in the micropump. The flow rate decreases if the fluid is dilatant. Also, it increases if the fluid is pseudoplastic. Moreover, the pressure which is needed to stop the electroosmotic flow rate in the micropump is calculated. Results show that, the back pressure has a slight change as the fluid has non-Newtonian behavior.     

A finite element based level-set method for multiphase flow applications

A numerical method for simulating incompressible two-dimensional multiphase flow is presented. The method is based on a level-set formulation discretized by a finite-element technique. The treatment of the specific features of this problem, such as surface tension forces acting at the interfaces separating two immiscible fluids, as well as the density and viscosity jumps that in general occur across such interfaces, have been integrated into the finite-element framework. Using a method based on the weak formulation of the Navier-Stokes equations has its advantages. In this formulation, the singular surface tension forces are included through line integrals along the interfaces, which are easily approximated quantities. In addition, differentiation of the discontinuous viscosity is avoided. The discontinuous density and viscosity are included in the finite element integrals. A strategy for the evaluation of integrals with discontinuous integrands has been developed based on a rigorous analysis of the errors associated with the evaluation of such integrals. Numerical tests have been performed. For the case of a rising buoyant bubble the results are in good agreement with results from a front-tracking method. The run presented here is a run including topology changes, where initially separated areas of one fluid merge in different stages due to buoyancy effects. Received: 1 March 1999 / Accepted: 17 June 1999     

Computerized methods for X-ray-based small bone densitometry

Animal models have been widely used to correlate in vivo changes in bone mineral density (BMD) with changes in disease state of bone. In small animal models, e.g. the hindlimb suspension model of bone loss, a non-invasive assessment of BMD is required. X-ray radiography has been surpassed in some cases by quantitative computed tomography (QCT) and dual X-ray absorptiometry (DEXA) quantitation. However, there are drawbacks in using the computerized methods, especially for small animals. In this paper, we present image-processing algorithms to quantitatively determine bone area and mineral density in digitized radiographs. Image calibration is based on a calibration step wedge, and the algorithm automatically detects the steps and computes the calibration data. In addition, we demonstrate how the algorithm can accurately determine the cortical outline of the bone and provide reliable data and statistics for small animal studies. A downloadable implementation example for the popular NIH Image package is provided.     

SPH simulation of selective withdrawal from microcavity

The selective withdrawal of weakly compressible fluids is investigated by smoothed particle hydrodynamics (SPH) with a revised model of surface tension. In our model problem, fluid is withdrawn from a two-dimensional microcavity through a narrow outlet above the interface of two immiscible fluids. The outflow boundary is implemented by a particular zone of fluid particles with prescribed velocity, together with the introduction of artificial boundary particles. Based on the average number density of fluid particles, the effective contribution of boundary particles is corrected for the compressible context. It is found that there exists a critical withdrawal rate for each initial interface height, beyond which the lower phase becomes entrained in a thin spout along with the upper phase. Besides, the Froude number with redefinition for this kind of multiphase flow could serve as a criterion of flow behavior. Furthermore, larger surface tension, smaller dynamical viscosity and density of the upper phase all lead to longer threshold time of formation of the spout state, and thus are favorable to the withdrawal of upper phase both in terms of higher efficiency and larger quantity.     

Towards a continuous microfluidic rheometer

In a previous paper we presented a way to measure the rheological properties of complex fluids on a microfluidic chip (Guillot et al., Langmuir 22:6438, 2006). The principle of our method is to use parallel flows between two immiscible fluids as a pressure sensor. In fact, in a such flow, both fluids flow side by side and the size occupied by each fluid stream depends only on both flow rates and on both viscosities. We use this property to measure the viscosity of one fluid knowing the viscosity of the other one, both flow rates and the relative size of both streams in a cross-section. We showed that using a less viscous fluid as a reference fluid allows to define a mean shear rate with a low standard deviation in the other fluid. This method allows us to measure the flow curve of a fluid with less than 250 μL of fluid. In this paper we implement this principle in a fully automated set up which controls the flow rate, analyzes the picture and calculates the mean shear rate and the viscosity of the studied fluid. We present results obtained for Newtonian fluids and complex fluids using this set up and we compare our data with cone and plate rheometer measurements. By adding a mixing stage in the fluidic network we show how this set up can be used to characterize in a continuous way the evolution of the rheological properties as a function of the formulation composition. We illustrate this by measuring the rheological curve of four formulations of polyethylene oxide solution with only 1.3 mL of concentrated polyethylene oxide solution. This method could be very useful in screening processes where the viscosity range and the behavior of the fluid to an applied stress must be evaluated.     

Model reduction via Chebyshev polynomials

Model reduction of a linear system characterized by transfer function is obtained by matching the Chebyshev spectra of the unit step responses of the original system and reduced model. In order to preserve the stable property of the original system, a combined method which uses conventional stable model reduction methods to determine the coefficients of the denominator polynomial of the reduced model and uses the Chebyshev spectrum matching to determine the coefficients of the numerator polynomial is proposed. Both methods are computer application oriented.