Flow behavior of liquid-solid coupled system of piezoelectric micropump

This paper employs a shallow water model and the finite element method to approximate periodical flows of a micropump to a two-dimensional thickness-averaged flow. A liquid-solid coupled system equation of the micropump is presented. Through the mode analysis of the liquid-solid coupled system, the first-order natural frequency, diaphragm vibration shape and amplitude-frequency relationship are obtained. The vibration response of the diaphragm is calculated when an external electric field is applied. Based on the thickness-averaged flow equation, the periodical flow of the micropump is studied using the finite volume method to investigate the flow behavior and flow rate-frequency characteristics. Numerical results indicate that an optimal working frequency can be obtained, at which the flow rate of the micropump achieves the maximum when the external electric voltage is fixed.     

无阀压电微流体泵工作特性与结构参数

根据平面无阀压电微流体泵的结构特点,采用厚度平均的浅水模型和有限元法,得到微流体泵液体－振动片耦合方程。耦合方程的模态分析给出硅片一阶模态自然频率和振型,以及硅片振幅－频率关系。在模态分析之后,加入压电力考察振动片响应、微泵流动特征和微泵流量。同时研究微泵结构参数(微泵压电片半径、扩散管长度、最小宽度、扩散张角)对微流体泵液—固耦合系统的自然频率、振动片振幅和微泵流量的影响,得出对微流体泵优化设计有重要意义的结果。     

Electro-magnetically actuated valveless micropump with two flexible diaphragms

We present a parallel dynamic passive valveless micropump, which consists of three layers-valve, diaphragm and electromagnetic coil. The valve is wetly etched in a silicon wafer, the diaphragm is a polydimethyl siloxane (PDMS) film spun on a silicon wafer with embedded permanent magnet posts, and the coil is electroplated on a silicon substrate. Under the actuation of the magnetic field of the coil, the flexible diaphragm can be displaced upwards and downwards. After analyzing magnetic and mechanical characteristic of the flexible membrane and direction-dependence of the nozzle, this paper designed a micropump. And the relative length (L/d) of the micropump's nozzle is 4. A 7×7 array of permanent magnetic posts is embedded in the PDMS film. Two diaphragms work in an anti-step mode, which can relieve the liquid shock and increase the discharge of the micropump. ANSYS and Matlab are adopted to analyze the actuation effect of the coil and the flow characteristic of the micropump. Results show that when actuated under a 0.3 A, 100 Hz current, the displacement of the diaphragm is more than 30 μm, and the discharge of the micropump is about 6 μL/s.     

NiTi/Si薄膜驱动微型无阀泵的系统研究

介绍了形状记忆合金 /硅 (Ni Ti/Si)复合膜驱动的微型无阀泵的结构及工作原理 ,采用 Matlab对微泵的压力 P和流量 Q进行了计算和仿真 ,并将仿真结果与实验结果进行了对比。通过分析驱动膜的驱动频率与泵的几何结构对微泵性能的影响 ,得到微泵的优化方案。     

悬臂输送管道流-固耦合动力学系统的直接解法

根据变分原理导出了输送管道(流—固耦合问题)自由振动的变分方程,采用直接解法求出了输送管道自由振动的固有频率和极限流速。     

基于MEMS的压电微泵建模与优化

以压电驱动的无阀微泵为研究对象,根据扩张管/收缩管的压力损失系数和连续方程,建立了无阀微泵的理论模型。利用有限元分析软件,建立了无阀微泵有限元模型,进行了耦合场仿真分析。模拟并分析了不同边界条件下驱动电压、电压频率、泵膜厚度、压电薄膜厚度和压电材料对无阀微泵输出特性的影响。仿真结果显示,无阀微泵具有很好的整流特性,并且驱动电压越大,输出特性越好。在局部固定边界条件下,当压电薄膜上施加电场强度为500 V/mm的驱动电压时,存在最优的压电薄膜厚度,使得微泵的输出流量最大。研究结果为无阀微泵的优化设计提供了依据。     

Analysis of stability and nonlinear response of rotor system with elliptical sliding bearing supports

Based on the variational constraint approach, the variational form of Reynolds equation in hydrodynamic lubrication is revised continuously to satisfy certain constraints in the cavitation zone of oil film field. According to the physical characteristic of oil film, an eight-node isoparametric finite element method is used to convert the revised variational form of Reynolds equation to a discrete form of finite dimensional algebraic variational equation. By this approach, a perturbance equation can be obtained directly on the finite element equation. Consequently, nonlinear oil film forces and their Jacobian matrices are calculated simultaneously, and compatible accuracy is obtained without increasing the computational costs. A method, which is a combination of predictor-corrector mechanism and Newton-Raphson method, is presented to calculate equilibrium position and critical speed corresponding to Hopf bifurcation point of bearing-rotor system, as by-product dynamic coefficients of bearing are obtained. The timescale, i.e., the unknown whirling period of Hopf bifurcation solution of bearing-rotor system is drawn into the iterative process using Poincaré-Newton-Floquet method. The stability of the Hopf bifurcation solution can be detected when estimating Hopf bifurcation solution and its periods. The nonlinear unbalanced T periodic responses of the system are obtained by using PNF method and path-following technique. The local stability and bifurcation behaviors of T periodic motions are analyzed by Floquet theory. Chaotic motions are analyzed by Lyapunov exponents. The numerical results revealed the rich and complex nonlinear behavior of the system, such as periodic, quasiperiodic, jumped solution, chaos, and coexistence of multisolution, and so on. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42(4): 88–95 [译自: 机械工程学报]     

摩擦噪声系统的振动特性研究

建立了一个往复滑动摩擦系统1∶1实体装配模型,采用有限元方法对该系统的振动特性进行研究,获得了系统的自然频率和振动模态。将得到的系统振动频率与系统的试验噪声的频率进行比较,发现它们的一些结果有很好的一致性。对系统的计算模态分析显示,发生噪声的模态同时具有切向和法向振动特征。     

局域共振型隔振系统的低频振动特性分析

为有效降低基体低频振动对精密仪器测量精度的影响,提出了周期布置吸振器的减振方式.建立了基体-隔振设备-吸振器系统的动力学模型,利用模态叠加法导出了系统耦合振动方程的解析解,并用有限元法进行了验证.获得了吸振器数量、参数对系统低频振动特性的影响规律,在吸振器总数一定的情况下,将其划分为包含不同数量振子的周期元胞.以低频段...     

Analysis of fluid induced vibration of cryogenic pipes in consideration of the cooling effect

The purpose of system analysis using fluid induced vibration is to identify the problems of the system in advance by analyzing the vibration behavior of the system excited by fluid flow. Fluid-induced vibration analysis methods, developed so far, generally use the numerical analysis method to analyze the fluid flowing inside the pipe and the infinitesimal elements at normal temperature on the basis of the governing equation obtained by applying Newton’s Second Law and the momentum equation. However, as the fluid temperature changes greatly at low temperature, fluid-induced vibration analysis methods for normal temperature cannot be applied. This study investigated methods of analyzing fluid-induced vibration in consideration of the cooling effect. In consideration of the changes in the properties of the fluid and system relative to temperature, vibration behavior was analyzed numerically by means of the equation of motion. As a result, the natural frequency of the system tends to change because of the changes of the properties of materials even when the flux is constant inside the pipe, and the vibration behavior of the system was compared to that in case of normal temperature to analyze how much influence the cooling effect has on the vibration behavior of the system. This paper was recommended for publication in revised form by Associate Editor Seockhyun Kim     

ZERO MODE NATURAL FREQUENCY AND NONLINEAR VIBRATION OF COUPLED LATERAL AND TORSION OF A LARGE TURBINE GENERATOR

Zero mode natural frequency (ZMNF) is found during experiments. The ZMNF and vibrations resulted by it are studied. First, calculating method of the ZMNF excited by electromagnetic in vibrational system of coupled mechanics and electrics are given from the view of magnetic energy. Laws that the ZMNF vanes with active power and exciting current are obtained and are verified by experiments. Then, coupled lateral and torsional vibration of rotor shaft system is studied by considering rest eccentricity, rotating eccentricity and swing eccentricity. Using Largrange-Maxwell equation when three phases are asymmetric derives differential equation of the coupled vibration. With energy method of nonlinear vibration, amplitude-frequency characteristics of resonance are studied when rotating speed of rotor equals to ZMNF. The results show that ZMNF will occur in turbine gen erators by the action of electromagnetic Because ZMNF varies with electromagnetic parameters, resonance can occur when exciting frequency of the     

Development of electrorheological chip and conducting polymer-based sensor

This paper presents the development of an integrated sensor using two types of smart materials: electrorheological (ER) fluids and conducting polymers (CPs). The developed ER chip worked as an actuator, and it was driven by different voltages and control frequencies. When the four electrodes are controlled synchronously, the diaphragm acts as a vibrator whose frequency can be adjusted in accordance with the frequency of the electrical signals. The response signals of the CP sensor were recorded, and its properties were analyzed. Experimental results show that the amplitude decreases monotonically when the frequency increases, owing to the time delay in the pressure buildup in the ER chip. However, the displacement fluctuation of the diaphragm below 20Hz can be detected clearly even if the value is very low. When the vibration frequency is larger than 20Hz, the CP sensor can hardly detect the displacement fluctuation. Thus, the upper limit frequency that the CP sensor can detect is about 20Hz. The practical applications of this microdevice are also discussed.     

Effects of fluid-structure interaction on trailing-edge noise

This study numerically investigates the effects of fluid-structure interaction (FSI) on the trailing-edge noise, particularly for the cases of wake instability and Karman vortex shedding. The trailing edge is modeled as a flat plate with an elastic cantilever end and its flow-induced vibration is solved by an eigenmode analysis with the Galerkin method. The flow and sound coupled in the FSI analysis are computed on the moving grid by a direct numerical simulation (DNS) procedure. The computed result of wake instability shows that when the first-eigenmode natural frequency ω _n of the cantilever is close to be resonant with the wake characteristic frequency ω _c , the sound pressure level (SPL) is significantly reduced by 20 dB at ω _n /ω _c =0.95, or increased by 15 dB at ω _n /ω _c =1.05, for all angles. For the Karman vortex shedding, a similar frequency modulation occurs via FSI, if ω _n is close to ω _c . The flow and acoustic details are somewhat different for this case but a considerable noise reduction was also possible for angles from −120° to +120°.     

Flexural vibration analysis of a sandwich beam specimen with a partially inserted viscoelastic layer

The flexural vibration characteristics of a sandwich beam system with a partially inserted viscoelastic layer were quantitatively studied using the finite element analysis in combination with the sine-sweep experiment. Asymmetric mode shapes of the flexural vibration were visualized by holographic interferometry, which agreed with those obtained by the finite element simulation. Effects of the length and the thickness of the partial viscoelastic layer on the system loss factor (η_s) and resonant frequency (f_r) were significantly large for both the symmetric and asymmetric modes of the beam system.     

重力全平衡提升式升船机的自振特性和稳定性分析

研究包括承船厢、提升钢索、平衡重、承船厢中的水和船舶在内的重力全平衡钢索提升式升船机系统，讨论其自振特性和稳定性；将这一系统模型化为流固耦合系统，将承船厢中的水处理为理想流体，采用伽辽金有限元方法离散，将承船厢及船舶视为刚体，考虑水和承船厢、船舶、提升钢索的相互作用，建立考虑流固耦合的动力学方程。为了求解该方程，对非对称的质量和刚度矩阵进行对称化处理；通过求解特征值问题，得到升船机系统的自振特性，讨论平衡重质量、提升钢索吊点位置、承船厢中船舶等对系统自振特性的影响。利用自振频率为零时系统失稳的力学概念，讨论使系统失稳的临界吊点位置。     

Fabrication and drive test of a peristaltic thermopnumatic PDMS micropump

This paper presenti, fabrication and drive test of a peristaltic PDMS micropump actuated by the thermopneumatic force The micropump consists of the three peristaltic-type actuator chambers with microheaters on the glass substrate and a microchannel connecting the chambers and the inlet/outlet port The micropump is fabricated by the spin-coating process, the two-step curing process, the JSR (negative PR) molding process, and etc The diameter and the thickness of the actuator diaphragm are 2 5 mm and 30 μm, respectively The meniscus motion in the capillary tube is observed with a video camera and the flow rate of the micro pump is calculated through the frame analysis of the recorded video data. The maximum flow rate of the micropump is about 0 36 μL/sec at 2 Hz for the zero hydraulic pressure difference when the 3-phase input voltage is 20 V.     

Study of fluid damping effects on resonant frequency of an electromagnetically actuated valveless micropump

As fluid flow effects on the actuation and dynamic response of a vibrating membrane are crucial to micropump design in drug delivery, this paper presents both a mathematical and finite-element analysis (FEA) validation of a solution to fluid damping of a valveless micropump model. To further understand the behavior of the micropump, effects of geometrical dimensions and properties of fluid on the resonant frequency are analyzed to optimize the design of the proposed micropump. The analytical and numerical solutions show that the resonant frequency decreases with the slenderness ratio of the diffuser and increases with the opening angle, high aspect ratio, and thickness ratio between the membrane and the fluid chamber depth. A specific valveless micropump model with a 6-mm diameter and 65-μm thickness polydimethylsiloxane (PDMS) composite elastic membrane was studied and analyzed when subjected to different fluids conditions. The resonant frequency of a clamped circular membrane is found to be 138.11 Hz, neglecting the fluid. For a gas fluid load, the frequency is attenuated by slightly shifting to 104.76 Hz and it is significantly reduced to 5.53 Hz when the liquid fluid is loaded. Resonant frequency remarkably shifts the flow rate of the pump; hence, frequency-dependent characteristics of both single-chamber and dual-chamber configuration micropumps were investigated. It was observed that, although the fluid capacity is doubled for the latter, the maximum flow rate was found to be around 27.73 μl/min under 0.4-A input current with an excitation frequency of 3 Hz. This is less than twice the flow rate of a single chamber of 19.61 μl/min tested under the same current but with an excitation frequency of 4.36 Hz. The proposed double-chamber model analytical solution combined with the optimization of the nozzle/diffuser design and assuming the effects of damping proved to be an effective tool in predicting micropump performance and flow rate delivery.     

DECOUPLING ACTUATORS WITHH∞ROBUST CONTROL FOR ACTIVELY ISOLATING VIBRATING MACHINES

A feedback controller designed to minimise the vibration transmitted to a flexible beam from a vibrating machine via two active isolation mounts is described. The state–space equation for the mechanical structure is obtained by performing modal analysis on the associated conservative structure.H_∞control methods are used to derive a decoupled (diagonal) controller which provides robustness against unmodeled high-order frequency dynamics and optimises the performance in terms of the frequency response shaping of the modal accelerations. The performances of the decoupled controller were found to be similar to those of the coupled (global) one.     

谐振式疲劳裂纹扩展试验振动系统质点质量的软测量方法

谐振式疲劳裂纹扩展试验振动系统的质点由多个不同形状、材质的部件组成,对质点质量进行直接测量有很大的局限性。提出了一种针对此类振动系统质点质量的软测量方法,建立了系统三自由度振动力学模型和动力学方程,推导得到关于系统固有频率、弹簧刚度与质点质量关系的系统频率方程,通过有限元方法计算出不同裂纹长度下试件的刚度,通过固有频率测量实验方法测出裂纹扩展到不同长度时系统的谐振频率,将不同裂纹长度时系统谐振频率值及相应试件刚度代入系统频率方程中,得到以待识别质点质量为未知数的超定方程组,求解超定方程组得到最小二乘解,并通过后续处理得到振动系统的主振质量和激振质量。为验证该方法,进行了相关实验。实验结果表明:主振质量测量的最大误差为6.76%,表明所提出方法具有理论意义和应用价值。     

钹型开槽式阀压电泵的设计

由于有阀压电泵内部阀体所受应力过大易导致阀体失效,本文提出了钹型开槽式截止阀来减小有阀压电泵内部阀体所受应力。基于钹型开槽式截止阀设计了有阀压电泵,分析了钹型开槽式阀压电泵的工作原理。对钹型开槽膜片进行了受力分析,研究了该压电泵的输出性能及耦合作用下的膜片应力。加工制作了钹型开槽式阀压电泵样机,建立了钹型开槽式阀压电泵的有限元模型,数值计算了流固耦合作用下的阀体应力值。计算结果表明:在压电泵正常输出的驱动频率范围内,当驱动频率为418Hz时,膜片所受应力的计算值也达到最大,为81.74 MPa。最后,进行了压电泵性能试验。试验结果显示:该压电泵的输出流量最大值和振子振幅最大值均出现在低频段;当驱动电压为160V,驱动频率为5Hz时,输出流量达到最大,为6.6g/min;驱动频率为4Hz时,压电振子振幅达到最大,为165.8μm。文中的研究验证了钹型开槽式阀体压电泵的有效性,并得出当钹型开槽式阀压电泵工作在低频段时,阀门所受应力远小于高频段时阀门的应力值。