Membrane finite element method for simulating fluid flow in porous medium

A new membrane finite element method for modeling fluid flow in a porous medium is presented in order to quickly and accurately simulate the geo-membrane fabric used in civil engineering. It is based on discontinuous finite element theory, and can be easily coupled with the normal Galerkin finite element method. Based on the saturated seepage equation, the element coefficient matrix of the membrane element method is derived, and a geometric transform relation for the membrane element between a global coordinate system and a local coordinate system is obtained. A method for the determination of the fluid flux conductivity of the membrane element is presented. This method provides a basis for determining discontinuous parameters in discontinuous finite element theory. An anti-seepage problem regarding the foundation of a building is analyzed by coupling the membrane finite element method with the normal Galerkin finite element method. The analysis results demonstrate the utility and superiority of the membrane finite element method in fluid flow analysis of a porous medium.

Flow-Induced Clogging in Microfiltration Membranes: Numerical Modeling and Parametric Study

Microfiltration membrane technology has been widely used in various industries for solid-liquid separation. However, pore clogging remains a persistent challenge. This study employs (CFD) and discrete element method (DEM) models to enhance our understanding of microfiltration membrane clogging. The models were validated by comparing them to experimental data, demonstrating reasonable consistency. Subsequently, a parametric study was conducted on a cross-flow model, exploring the influence of key parameters on clogging. Findings show that clogging is a complex phenomenon affected by various factors. The mean inlet velocity and transmembrane flux were found to directly impact clogging, while the confinement ratio and cosine of the membrane pore entrance angle had an inverse relationship with it. Two clog types were identified: internal (inside the pore) and external (arching at the pore entrance), with the confinement ratio determining the type. This study introduced a dimensionless number as a quantitative clogging indicator based on transmembrane flux, Reynolds number, filtration time, entrance angle cosine, and confinement ratio. While this hypothesis held true in simulations, future studies should explore variations in clogging indicators, and improved modeling of clogging characteristics. Calibration between numerical and physical times and consideration of particle volume fraction will enhance understanding.

A novel four-node quadrilateral element with continuous nodal stress

Formulation and numerical evaluation of a novel four-node quadrilateral element with continuous nodal stress（Q4-CNS）are presented.Q4-CNS can be regarded as an improved hybrid FE-meshless four-node quadrilateral element（FE-LSPIM QUAD4）, which is a hybrid FE-meshless method.Derivatives of Q4-CNS are continuous at nodes, so the continuous nodal stress can be obtained without any smoothing operation.It is found that,compared with the standard four-node quadrilateral element（QUAD4）,Q4- CNS can achieve significantly better accuracy and higher convergence rate.It is also found that Q4-CNS exhibits high tolerance to mesh distortion.Moreover,since derivatives of Q4-CNS shape functions are continuous at nodes,Q4-CNS is potentially useful for the problem of bending plate and shell models.

Quadrature Element Vibration Analysis of Arbitrarily Shaped Membranes

The aim of the present study is to develop an efficient weak form quadrature element for free vibration analysis of arbitrarily shaped membranes.The arbitrarily shaped membrane is firstly mapped into a regular domain using blending functions,and the displacement in the element is assumed as the trigonometric functions.Explicit formulations are worked out for nodes of any type and a varying number of nodes.For verifications,results are compared with exact solutions and data obtained by other numerical methods.It is demonstrated that highly accurate frequencies can be obtained with a small number of nodes by present method.

Patterned catalyst layer boosts the performance of proton exchange membrane fuel cells by optimizing water management

Mass transport is crucial to the performance of proton exchange membrane fuel cells,especially at high current densities.Generally,the oxygen and the generated water share same transmission medium but move towards opposite direction,which leads to serious mass transfer problems.Herein,a series of patterned catalyst layer were prepared with a simple one-step impressing method using nylon sieves as templates.With grooves 100μm in width and 8μm in depth on the surface of cathode catalyst layer,the maximum power density of fuel cell increases by 10%without any additional durability loss while maintaining a similar electrochemical surface area.The concentration contours calculated by finite element analysis reveal that the grooves built on the surface of catalyst layer serve to accumulate the water nearby while oxygen tends to transfer through relatively convex region,which results from capillary pressure difference caused by the pore structure difference between the two regions.The separation of oxidant gas and generated water avoids mass confliction thus boosts mass transport efficiency.

Design and application of structural health monitoring system in long-span cable-membrane structure

Cable-membrane structures have small rigidity and are highly sensitive to wind. Structural health monitoring is necessary to ensure the serviceability and safety of the structure. In this research, the design method of a structural health monitoring system is using the characteristics of a cable-membrane structure. Taking the Yueyang Sanhe Airport Terminal as an example, a finite element model is established to determine the critical structural components. Next, the engineering requirements and the framework of the monitoring system are studied based on the results of numerical analysis. The specific implementation of the structural health monitoring is then carried out, which includes sensor selection, installation and wiring. The proposed framework is successfully applied to the monitoring system for the Yueyang Airport terminal building, and the synchronous acquisition of fiber Bragg grating and acceleration sensor signals is implemented in an innovative way. The successful implementation and operation of structural health monitoring will help to guarantee the safety of the cablemembrane structure during its service life.

Analysis on nonlinear wind-induced dynamic response of membrane roofs with aerodynamic effects

Based on the characteristics of membrane structures and the air influence factors,this paper presented a method to simulate the air aerodynamic force effects including the added air mass,the acoustic radiation damping and the pneumatic stiffness.The infinite air was modeled using the acoustic fluid element of commercial FE software and the finite element membrane roof models were coupled with fluid models.A comparison between the results obtained by FE computation and those obtained by the vibration experiment for a cable-membrane verified the validity of the method.Furthermore,applying the method to a flat membrane roof structure and using its wind tunnel test results,the analysis of nonlinear wind-induced dynamic responses for such geometrically nonlinear roofs,including the roof-air coupled model was performed.The result shows that the air has large influence on vibrating membrane roofs according to results of comparing the nodal time-history displacements,accelerations and stress of the two different cases.Meantime,numerical studies show that the method developed can successfully solve the nonlinear wind-induced dynamic response of the membrane roof with aerodynamic effects.

Method to analyze wrinkled membranes with zero shear modulus and equivalent stiffness

To solve the problems of divergence,low accuracy and project application of membrane wrinkling analysis,an analysis method of zero shear modulus and equivalent stiffness was proposed.This method is an improvement to the previous method (Method I) of local coordinate transposition and stiffness equivalence.The new method is derived and the feasibility is theoretically proved.A small-scale membrane structure is analyzed by the two methods,and the results show that the computational efficiency of the new method (Method II) is approximately 23 times that of Method I.When Method II is applied to a large-scale membrane stadium structure,it is found that this new method can quickly make the second principal stress of one way wrinkled elements zero,and make the two principal stresses of two-way wrinkled elements zero as well.It could attain the correct load responses right after the appearance of wrinkled elements,which indicates that Method II can be applied to wrinkling analysis of large-scale membrane structures.

Prediction of wrinkles in the membrane

This paper presents an analytical approach for predicting the detailed out-of-plane wrinkle deformation that formed in the membrane. The analytical wrinkle model is based on the assumption that the membrane is able to resist small compressive stress once it has wrinkled. This model is developed for the cases of the rectangular membrane subjected to pure shear and local tension by using the equilibrium equation of the membrane in the deformed configuration. Predictions from this model are compared with the finite element simulation based on the nonlinear buckling finite element method and the results are found to be accurate.

Fabrication of anodized aluminum oxide membrane with nanometer pores

The pure aluminum and Al Mg Mn alloy were anodized in 4%, 10% and 18.5% phosphoric acid solution, respectively. As for pure Al, the maximum thickness of anodized aluminum oxide (AAO) membrane, 216 nm, is obtained by being anodized in 4% solution. Its average pore diameter is around 70 nm, and pore density exceeds 10 10 /cm 2. Under the same technology condition, the membrane thickness decreases with increment of electrolyte content. TEM images show that element Mg or Mn added into aluminum alloy can damage the integration of AAO membrane. During anodizing of aluminum, the formed oxide layer is amorphous. After being annealed at 600 ℃ for 24 h, it is still amorphous. However, when membrane is annealed at 930 ℃, the amorphous oxide begins to transform to γ Al 2O 3 .

骨架膜装配式节点设计与承载力分析

提出的骨架膜结构装配式节点具有构造简单、预制程度高、便于现场装配、可以调节消减加工误差、适应各种形状的骨架膜结构、传力清晰等特点。基于Hertz接触理论分析了该节点的关键承载结构——销轴连接的应力分布形式并与有限元分析相互印证。基于有限元分析得出了该节点中杆件与耳板最佳的连接方式,对该节点的三维模型进行简化并建立有限元模型,计算了该节点的极限承载能力,得到其破坏形式并与同规格的空间相贯焊接钢管节点进行对比。结果表明:该装配式节点的失效由下弦杆控制,满足“强节点,弱杆件”的设计要求;该装配式节点的极限承载能力为设计荷载的2.95倍,与同规格的空间相贯焊接钢管节点几乎相同,有充足的安全余量,可以更加灵活地应用于各种建筑结构中。

质子交换膜燃料电池直流道内液滴传输研究

建立质子交换膜燃料电池(PEMFC)的二维直流道模型,分析液滴在流道内的产生、破裂及传输全过程,探究进气速度、气体扩散层表面亲疏水性以及挡板结构参数等关键性因素对液滴传输特性的影响。仿真结果表明,提高进气速度有助于强化液滴的去除效果,但过高的气体流速会将液滴推向气体扩散层表面,造成液滴累积;亲水性较强的气体扩散层表面导致液滴严重坍塌形变,堵塞气体扩散层孔隙;液滴在疏水性气体扩散层表面流动速度相对较快,壁面附着力小,利于流道排水;增大挡板堵塞率可提高挡板下方及后方区域气体流速,提高液滴吹扫能力;挡板表面亲疏水性对流道内液滴去除效果影响较弱。

基于力密度的径向肋式索膜反射面天线形态设计

针对空间索膜结构的初始形态设计问题,提出基于力密度方法和控制索网网格面积大小的方法来对边界拉索张力设计和索网形状设计的天线找形迭代策略。首先将薄膜反射面离散为三角形膜单元,得到膜单元的等效力密度,结合索网结构特点,得到索网和薄膜的静力平衡方程。保证索网所有内部索段的张力相等,同时通过控制网格面积大小实现边界索段张力设计。对前索网形状进行设计,根据前索网的抛物面方程,更新前索网自由节点坐标,进而重新调整竖向索张力,同时控制网格面积大小,通过优化迭代过程,实现天线的形态设计。通过径向肋式索膜反射面天线算例表明,该方法能够得到满足形状和张力分布的设计结果。

鼓膜穿孔导致听力下降的有限元模型分析

目的探讨鼓膜穿孔导致听力下降的机制。方法通过有限元分析法(finite element analysis,FEA)构建全耳有限元模型并验证;参照实际鼓膜穿孔病例,创建个性化的鼓膜穿孔有限元模型,模拟鼓膜穿孔导致的听力损失;使用基底膜的位移响应与基线的差异来模拟听力损失情况,分析中耳各个组分对听力损失的贡献程度,探讨鼓膜穿孔导致听力下降的机制。结果如果将圆窗膜和中耳腔的耦合去掉,将导致低频约40 dB的听力下降,而高频段基本与基线情况下鼓膜穿孔所导致的听力损失持平;去除鼓膜内侧面和中耳腔气体的耦合,可部分减轻低频听力损失,而高频听力损失加重;切断外耳道气体和中耳腔气体之间的连续性,低频听力损失加重;但是去除圆窗膜和中耳腔之间耦合关系并且去除中耳腔气体和鼓膜内侧面的连接后,原先低频的40 dB听力损失将会恢复到10 dB左右;而去除中耳腔气体和听骨链之间的耦合,对听力损失无明显影响。结论鼓膜穿孔导致听力下降的主要机制是鼓膜穿孔本身所导致的传声效能降低,以及鼓膜内外声压差的降低;圆窗膜处声压的增加可以部分弥补鼓膜穿孔所导致的听力损失。

改进型金字塔状夹芯板耦合MAM结构的降噪设计与研究

为解决薄膜型声学超材料(membrane-type acoustic metamaterial,MAM)低频区间隔声频段较窄、耐久性差以及抗风险能力弱的问题,探讨MAM在变压器降噪领域的应用,现设计出一种金字塔状夹芯板和MAM耦合的降噪结构。采用有限元法研究耦合结构的隔声性能和声振特性,建立结构的声固耦合模型,分析结构的声传递损失和振动模态,并探究影响结构降噪的因素。研究表明,耦合结构有着优秀的中低频宽带隔声特性,且可以通过调整薄膜和薄板的参数改变结构的隔声特性。优化后的结构在110 kV变压器主噪声频点上的隔声量均能超过110 dB。

小型束式中空纤维膜元件制作方法初探

为了提高膜生物反应器中膜的安装和更换效率,中空纤维膜在使用前通常先被制成膜元件,再组装成膜组件,以膜组件的形式安装在膜生物反应器中。然而,工程上制作处理大水量的中空纤维膜元件的设备并不适合制作实验室研究所需的处理水量较小的膜元件。为满足实验室研究对中空纤维膜元件的需求,本研究探讨了一种利用商用聚偏氟乙烯中空纤维丝制作小型束式中空纤维膜元件的方法,成功制作出可快速组装和拆卸的中空纤维膜元件。该小型中空纤维膜元件具有制作方法简单、成本低廉、封装效果好、成功率高,可根据实际情况灵活控制膜元件规模等优点。为研究膜污染机理使用的实验室规模膜分离系统提供了一种膜元件制作的新方法和新思路。

多孔介质布膜元件对水膜除尘器除尘性能的影响

通过实验,研究了多孔介质布膜元件对水膜除尘器除尘效率的影响,讨论了进气量、用水量、气水比对除尘效率的作用效果。在此基础上,采用计算流体力学DPM模型,研究了进气量和颗粒粒径对除尘效率的影响。研究表明,在除尘实验中,采用多孔介质布膜元件可有效提高除尘效率,用水量越低,提高效果越明显;进气量和进水量对除尘效率具有显著的正向影响,但进气量的影响要大于进水量;不论是否存在多孔介质,除尘效率在气水比为21 m 3/kg达到最大值。模拟结果显示,在实验最大风量的条件下,对粒径94.55μm及以上的颗粒,具有100%的除尘效果;对于粒径68.58μm及以上的颗粒,能具有良好的除尘效率,数值可以在90%以上。

Sulfonated poly(aryl ether ketone sulfone)modified by polyoxometalates LaW_(10) clusters for proton exchange membranes with high proton conduction performance

Polyoxometalates(POMs)are classified as solid superacids which can exhibit notable proton conductivity,making them a promising functional inorganic filler for enhancing the proton conductivity of proton exchange membranes(PEMs).In this study,a series of hybrid membranes were obtained by molecular-level hybridization of Weakley-type POM Na_(7)H_(2)LaW_(10)O_(36)(LaW_(10))clusters into sulfonated poly(aryl ether ketone sulfone)(SPAEKS).All hybrid membranes exhibited greater proton conductivity than the pristine membrane in the 30–80℃temperature range.When the doping amount of LaW 10 reached 7 wt.%,the proton conductivity of M-LaW 10^(-7)achieved 64 mS·cm^(−1)at 80℃.Lanthanide ions'high coordination number property and variable coordination environment can aid to attract more water molecules from the environment.LaW 10 and these bound water can construct denser hydrogen bonds with–SO_(3)H of SPAEKS.These intensive hydrogen bonds will facilitate the constitution of more continuous proton transport channels,and improve the proton conductivity of the hybrid membrane.This work off ers a fresh approach to using POMs containing rare-earth components in PEMs.

用有限元模拟方法研究阶层式多孔薄膜几何参数对水通量的影响

通过系统改变阶层式多孔薄膜大孔和小孔的孔径及孔隙率等几何参数,用有限元模拟方法研究薄膜通量与相关几何参数之间线性或非线性的定量关系.模拟结果表明,在弯曲孔道基体中添加球形空穴形成阶层式多孔结构后,可使薄膜水通量提升约为原来的171%.对于弯曲孔道,单纯增加其数量可使水通量线性提升,单纯增大其孔径可使水通量以指数函数形式提升.对于球形空穴,单纯增加其数量或单纯增大其孔径,水通量均以指数函数形式提升.此外,球形空穴的水通量提升作用还依赖于它与弯曲孔道基体网格的相对尺寸,通过调节制备条件可提升分离膜材料的性能.

基于在线监测数据的水库围坝渗流安全分析

以济南市济阳区稍门平原水库西坝为例,通过对测压管水位在线监测数据整理分析,采用有限元法对大坝复合土工膜反演等效渗透系数,重新复核大坝渗流安全。结果表明:测压管水位与库水位变化趋势一致,正相关性较好,实测数据可靠性高;坝体渗流正常稳定,无明显趋势性变化;各工况条件下的坝基水力比降、逸出点比降均小于允许比降,大坝渗流稳定性满足要求。