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.

A NEW QUADRILATERAL THIN PLATE ELEMENT BASED ON THE MEMBRANE-PLATE SIMILARITY THEORY

A new effective path has been proposed to formulate thin plate element by using the similarity theory between plane elasticity and plate bending. Because of avoiding the difficulty of c(1) continuity, the construction of thin plate elements becomes easier. The similarity theory and its applications were discussed more deeply, and a new four nodes, sixteen D. O. F. ( degree of freedom) thin plate element was presented on the base of the similarity theory. Numerical results for typical problems show that this new element can pass the patch test and has a very good convergence and a high precision.

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.

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.

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.

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 .

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.

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。

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。

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。

索膜反射面可展开天线的形态设计

为研究金属反射网和索网的张紧状态对可展开天线形面精度的影响,考虑支撑桁架变形对索膜反射面可展开天线进行形态设计研究。金属反射网可看作一类薄膜结构,由于金属反射网和索网均需施加预张力来达到一定的刚度,因此首先基于索膜结构力密度方程进行形态设计,使其在自身预张力和外载作用下达到满足要求的形状和精度;索膜结构的张拉作用会导致桁架变形,造成再平衡后索膜反射面形面精度的降低和张力分布不合理,因此,需要建立天线整体的非线性有限元模型;对天线模型进行迭代修正,最后得到满足要求的张力设计变量和天线构型。最后通过相应算例,验证了方法的正确性。

静电成形薄膜反射面天线的裁剪设计

该文通过裁剪和拼接平面薄膜片来对静电成形薄膜反射面天线的表面进行设计制作。由于抛物面型薄膜反射面是一个不可展开表面,通常由许多平面薄膜片制作而成,将不可避免地降低反射面表面的精度。因此,需要详细地分析裁剪和拼接过程对反射面表面精度的影响,从而获得设计需要的表面精度。该文基于旋转抛物面的无矩理论建立了工作状态的反射面模型,采用常应变三角形单元离散反射面,建立了反射面的展平和拼接有限元模型。将同口径反射面沿经线划分若干组不同数量子曲面,通过子曲面进行展平和拼接数值仿真分析,对薄膜反射面进行裁剪设计。最后,制作了0.55 m口径的薄膜反射器,并进行了摄影测量实验。验证了该方法的有效性,并讨论了制造误差的影响。

单层拉索式ETFE膜结构制作安装关键技术

结合实际工程应用,介绍单层拉索式ETFE膜结构安装技术特点与难点及其安装关键技术。采用膜结构逆向建模、双轴试验、现场组合安装、膜结构张拉等技术,实现了单层透明ETFE膜结构精准安装。实践表明,该技术节约了劳动力,缩短了工期,安装质量高,施工过程安全可靠,经济效果显著。

某充气膜结构承载能力分析及评估

以某实际工程为例,介绍了某充气膜结构的检查要点和承载能力评估方法。现场对充气膜结构的控制点位、充气系统、膜面性能、金属构件及连接节点等进行检查,并采用有限元软件3D3S对该充气膜进行建模计算,结果表明:该充气膜结构承载能力能满足规范要求,但是索与钢筋混凝土支承构件的连接构造不满足规范要求,应进行处理。本案例可为其它类似工程提供参考。