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991.
Numerical modeling of multiphase flows in microfluidics and micro process engineering: a review of methods and applications 总被引:2,自引:1,他引:1
Martin Wörner 《Microfluidics and nanofluidics》2012,12(6):841-886
This article presents a comprehensive review of numerical methods and models for interface resolving simulations of multiphase
flows in microfluidics and micro process engineering. The focus of the paper is on continuum methods where it covers the three
common approaches in the sharp interface limit, namely the volume-of-fluid method with interface reconstruction, the level
set method and the front tracking method, as well as methods with finite interface thickness such as color-function based
methods and the phase-field method. Variants of the mesoscopic lattice Boltzmann method for two-fluid flows are also discussed,
as well as various hybrid approaches. The mathematical foundation of each method is given and its specific advantages and
limitations are highlighted. For continuum methods, the coupling of the interface evolution equation with the single-field
Navier–Stokes equations and related issues are discussed. Methods and models for surface tension forces, contact lines, heat
and mass transfer and phase change are presented. In the second part of this article applications of the methods in microfluidics
and micro process engineering are reviewed, including flow hydrodynamics (separated and segmented flow, bubble and drop formation,
breakup and coalescence), heat and mass transfer (with and without chemical reactions), mixing and dispersion, Marangoni flows
and surfactants, and boiling. 相似文献
992.
Magalie De Ville Philippe Coquet Philippe Brunet Rabah Boukherroub 《Microfluidics and nanofluidics》2012,12(6):953-961
Convenient for both biologists and MEMS designers, Polydimethylsiloxane (PDMS) polymer is intensively investigated for its
biocompatibility, transparency, high resistance under plasma treatment, flexibility and resistance to high temperature. However,
for microfluidic applications, the fabrication of PDMS circular channels is difficult to achieve except by wire moulding.
In this article, we present a simple, fast and low-cost fabrication method which can be applied out of clean-room environment.
It is based on the deposition of alginic acid sodium salt aqueous solution, enabling the formation of a liquid cylinder on
the most hydrophilic part of a hydrophilic/hydrophobic patterned surface. We experimentally studied the interaction between
liquid rivulets and surfaces presenting a contrast of wettability and/or a stepwise texture. Subsequent moulding of the half-cylinder
of liquid produces round PDMS microfluidic channels. The optimal parameters for hydrophilic/hydrophobic patterns have then
been applied to produce the roundest possible channels. The realisation of both straight channels 300–500 μm wide, 1 cm long
and 75° tangent chord angle at best, and Y-shaped channels with the same dimensions and 55° TCA is demonstrated. 相似文献
993.
This paper presents a two-dimensional (2D)-based approach to the problem of output feedback repetitive control for uncertain
discrete-time systems. It is shown first how the proposed repetitive control scheme can be equivalently formulated in the
form of a distinct class of 2D system. Then sufficient conditions for the existence of output feedback control law are derived
in terms of linear matrix inequality (LMI), and the control law matrices are characterized by the feasible solutions to this
LMI. Moreover, an optimization problem is introduced to efficiently solve the optimal output feedback control law by minimizing
the upper bound of a given cost function. Compared with the commonly used 1D-based method, the proposed approach increases
the degree of freedom of controller design by not only including in the scheme an output feedback gain but also a feed forward
one which can be simultaneously solved using the 2D-based procedures presented in the paper. Finally, a numerical example
is provided to demonstrate the effectiveness of the proposed method. 相似文献
994.
Ho-Chan Kim Hardian Reza Dharmayanda Taesam Kang Agus Budiyono Gigun Lee Widyawardana Adiprawita 《International Journal of Control, Automation and Systems》2012,10(1):88-101
Rigorous control synthesis for an unmanned aerial vehicle necessitates the availability of a good, reasonable model for such
a vehicle. The work reported in this paper focuses on the modeling of a rotary unmanned aerial vehicle (RUAV) and the development
of a robust controller that can handle parameter uncertainties and disturbances. The parameters of the plant model are obtained
through the use of the prediction error method with real flight data. The response of the identified linear model shows a
good match with the measured flight data. The H
∞ control scheme is applied to obtain a robustly stable controller using the identified model. The proposed controller is analyzed
using frequency-domain analysis and time-domain simulations. The performance of the proposed H
∞ controller is better than that of the conventional proportional derivative controller in that the proposed controller has
a shorter settling time and less overshoot. Furthermore, the degradation of the proposed controller performance is negligible
and stability is maintained when the input gains to the plant are doubled, which demonstrates the good performance and robustness
of the controller. 相似文献
995.
An investigation into vehicle rollover prevention by coordinated control of active anti-roll bar and electronic stability program 总被引:1,自引:0,他引:1
Seongjin Yim Kwangki Jeon Kyongsu Yi 《International Journal of Control, Automation and Systems》2012,10(2):275-287
This paper presents a method for designing a controller that uses an active anti-roll bar (AARB) and an electronic stability program (ESP) for rollover prevention. ESP with longitudinal speed control (LSC) can carry out active braking to reduce vehicle speed and lateral acceleration to prevent a rollover. To enhance the rollover prevention capability of the ESP, an AARB is adopted. The controller for the AARB was designed based on linear quadratic (LQ) static output feedback (SOF) control methodology, which attenuates the effect of lateral acceleration on the roll angle and roll rate by control of the suspension stroke and the tire deflection of the vehicle. Although this AARB significantly increases ride comfort and rollover prevention, it has a drawback — the vehicle loses its maneuverability. Therefore, the ESP with LSC is used to overcome this drawback. Simulations showed that the proposed method was effective in preventing a rollover. 相似文献
996.
An important direction of metamodeling research focuses on developing methods which can iteratively improve the accuracy of
the metamodel. The intention of these kinds of strategies is to use a space reduction strategy to lead response surface refinement
to a smaller design space; and new sample points are commonly generated near the optimum. The potential risk is that some
characteristics of given problems might be lost, especially for nonlinear problems. Therefore, a novel metamodel-assisted
optimization called “Min–Median–Max” (M3) is proposed. This algorithm classifies sample points into three categories (maximum,
median and minimum) based on corresponding objective function values, new sample points should be generated by considering
combination of three kinds of samples. In order to avoid local convergence and control size of sample points, particle swarm
optimization (PSO) algorithm and radial basis function (RBF) metamodeling technique are integrated to implement the suggested
M3 strategy. To validate the performance of the M3 strategy, multiple mathematical test functions are used for evaluating
the accuracy and efficiency. As a practical engineering application, drawbead design of a stamping system is optimized. The
results demonstrate applicability and effectiveness of the M3 algorithm. 相似文献
997.
本文给出的有理分式反Z变换方法可以同时给出因果和逆因果两种序列.由于它避免了现有三种反Z变换方法所必需的确定分式极点的困难及误差,所以使用起来较为方便和精确.它可用来研究子波信号的延迟性质与系统(如滤波器)稳定性和可逆性,还可用来求解线性系统的差分方程,确定分式零点与极点的定位范围. 相似文献
998.
999.
In finite labelled transition systems the problems of deciding strong bisimilarity, observation equivalence and observation congruence areP-complete under many—oneNC-reducibility. As a consequence, algorithms for automated analysis of finite state systems based on bisimulation seem to be inherently sequential in the following sense: the design of anNC algorithm to solve any of these problems will require an algorithmic breakthrough, which is exceedingly hard to achieve. 相似文献
1000.
由于RGB颜色空间不能很好贴近人的视觉感知,同时也缺少对空间结构的描述,因此采用兼顾颜色信息和空间信息的高斯颜色模型以获取更全面的特征,提出了一种基于高斯颜色模型和多尺度滤波器组的彩色纹理图像分类法,用于瓷器碎片图像的分类。首先将原始图像的RGB颜色空间转换到高斯颜色模型;再用正规化多尺度LM滤波器组对高斯颜色模型的3个通道构造滤波图像,并借助主成分分析寻找主特征图,接着选取各通道的最大高斯拉普拉斯和最大高斯响应图像,与特征图联合构成特征图像组用以进行参数提取;最后以支持向量机作为分类器进行学习和分类。实验结果表明,与基于灰度的、基于RGB模型的和基于RGB_bior 4.4小波的方法相比,本文方法具有更好的分类结果,其中在Outex纹理图像库上获得的分类准确率为96.7%,在瓷片图像集上获得的分类准确率为94.2%。此方法可推广应用到其他彩色纹理分类任务。 相似文献