点面电极系统低频流体驱动机理

为了弥补传统交流电动力学理论在解释微流体反向流动方面的不足,开发了一种新型三维点面电极系统并进行微流体驱动实验,分析了低频条件下电化学、交流电热等因素对微流体驱动的影响.实验结果表明,点面电极系统中广频范围内(10～3×106Hz)的微流体流动方向均为由点电极流向面电极,这一现象与利用交流电渗理论预测的流体流动方向相反.实验验证了低频条件下电化学反应在流体流动中的重要作用.结果表明,电化学反应是点面电极系统中低频条件下微流体流动现象的主要因素.

点面电极系统高频流体驱动机理

为了研究交流电场作用下微流体高频驱动机理,以点面电极系统为基础,进行了高于驰豫频率范围的交流电动微流体驱动实验,发现了这一范围内的明显流体流动现象.指出电热效应是点面电极系统中产生高频微流体流动的主要因素,分析了电热效应对点面电极系统中电导率分布的影响.以点面电极系统中的电荷守恒方程、传导与扩散方程、Navier-Stokes方程以及热对流和传导方程为基础,对点面电极系统高频流体驱动过程进行耦合及数值仿真分析,给出了点面电极系统中电场、温度场以及速度场的分布曲线.分析了电压、频率等因素对于高频流体驱动速度的影响,并与实验结果进行了对比分析.结果表明,点面电极系统中,交流电热效应导致的点面电极之间的电导率梯度与电场的综合作用,是该系统高频流体驱动的主要因素,机理分析与实验结果具有较好的一致性.

Electrohydromechanical analysis based on conductivity gradient in microchannel

Fluid manipulation is very important in any lab-on-a-chip system. This paper analyses phenomena which use the alternating current （AC） electric field to deflect and manipulate coflowing streams of two different electrolytes （with conductivity gradient） within a microfluidic channel. The basic theory of the electrohydrodynamics and simulation of the analytical model are used to explain the phenomena. The velocity induced for different voltages and conductivity gradient are computed. The results show that when the AC electrical signal is applied on the electrodes, the fluid with higher conductivity occupies a larger region of the channel and the interface of the two fluids is deflected. It will provide some basic reference for people who want to do more study in the control of different fluids with conductivity gradient in a microfluidic channel.

A model of bone adaptation as a topology optimization process with contact

Topology optimization is presently used in most diverse scientific, technologic and industrial areas, including biomechanics. Bone remodelling models and structural optimization has mutually provided inspiration for new developments in biomechanics and biomedicine. Considering that bone has the ability to adapt its internal structure to mechanical loading (Wolff’s law and Roux’s paradigm), it is possible to model the behaviour of the bone structure by the use of a topology optimization methodology whose optimization variables can be the relative densities and the orthotropic directions. In this work, the internal bone adaptation of a proximal femur is considered. The bone-remodelling scheme is numerically described by a time-dependent evolutionary procedure with anisotropic material parameters. The remodelling rate equation is obtained from the structural optimization task of maximizing the stiffness subject to a biological cost associated with metabolic maintenance of bone tissue in time. The situation of multiple load conditions is considered for a three-dimensional finite element model of the proximal femur. The bone density distribution of a real femur is used as the initial design for the onset of the remodelling mechanism. Examples of bone adaptation resulting from load changes are presented. The three-dimensional finite element model of the proximal femur with initial bone density distribution was adapted to implant a cementless stem. A remeshing technique is used to assign the bone relative density distribution to the new geometry and mesh. The time adaptation of the bone is assessed considering contact with friction at the bone-stem interface. Results of bone density evolution and osteointegration distribution are obtained.

Force criterion of different electrolytes in microchannel

The control and handling of fluids is central to many applications of the lab-on-chip. This paper analyzes the basic theory of manipulating different electrolytes and finds the two-dimensional model. Coulomb force and dielectric force belonging to the body force of different electrolytes in the microchannel were analyzed. The force criterion at the interface was concluded, and testified by the specific example. Three basic equations were analyzed and applied to simulate the phenomenon. The force criterion was proved to be correct based on the simulation results.

Generation and Control of Turbulences in a Wind Tunnel

In this paper, the generation and control of turbulences in a wind tunnel, for design, analysis and testing of test objects are proposed. Modifications to the wind tunnel are made in order to generate the turbulences in the test chamber. Specifically, for the turbulence analysis, the reflective symmetry concept is used in order to group the different turbulences cases generated in the wind tunnel test chamber. The Ansys software is used in order to model and analyze the wind tunnel. Specific platform or module known as Fluent is used for the analysis of the turbulence generated in the wind tunnel. To design proposal of a wind tunnel capable to generate and controlling turbulences is exposed in this paper. For this, the controller design and verification are performed by means of simulations. To obtain the control law structure, the inversion concept is used. The proposed control law is validated via a co-simulation implemented in the Simplorer module, with the aim of combining the power electronics part, controller and engine, with the proposed model wind tunnel.

Fiber Optic Intensity-Modulated Sensors： a Review in Biomechanics

Fiber optic sensors have a set of properties that make them very attractive in biomechanics. However, they remain unknown to many who work in the field. Some possible causes are scarce information, few research groups using them in a routine basis, and even fewer companies offering turnkey and affordable solutions. Nevertheless, as optical fibers revolutionize the way of carrying data in telecommunications, a similar trend is detectable in the world of sensing. The present review aims to describe the most relevant contributions of fiber sensing in biomechanics since their introduction, from 1960s to the present, focusing on intensity-based configurations. An effort has been made to identify key researchers, research and development （R＆D） groups and main applications.