基于流阻率的吸声材料声学性能研究

运用加权残值法建立了两种介质相互作用的声学有限元计算方程式.基于多孔纤维材料等效流体的经验公式,分析了复声速和复密度相对流阻率的变化规律.针对不同多孔吸声材料结构布置形式,采用上述有限元计算方程和经验公式,计算得到随流阻率变化的传递损失.结果表明,空气滤清器型结构传递损失随流阻率增加而增加;阻性消声器型结构传递损失随流阻率而变化的规律复杂,在计算频段内存在峰值.

纤维多孔金属的流阻率分形模型研究

为了揭示纤维多孔金属吸声材料的流阻率与其孔隙率、孔直径以及孔的弯曲度等主要几何参数之间的变化规律,给纤维多孔金属吸声材料的结构设计提供基本的理论指导,提出了一种流阻率分形模型。通过对纤维多孔金属的孔隙结构进行分形处理,结合材料内部空气流体学分析,首先获得了流经纤维多孔金属材料截面总的空气流量Q的表达式,该表达式是最大平均孔径λmax、曲线分形维数DT和孔面积分形维数Df的函数,其次结合纤维多孔金属吸声材料流阻率的公式,获得了流阻率分形模型。模型理论计算值与实验测试值的最大偏差为13.9%,最小偏差为7.6%,平均偏差为10.6%,验证了该理论模型的可靠性。分析结果表明:随着孔隙率Φ的增大,纤维多孔金属吸声材料的流阻率减小;Φ和DT一定时,流阻率随着Df的增大而减小;Φ和Df一定时,流阻率随着DT的增大而增大。与通过实验确定流阻率的经验公式相比,文中所建流阻率分形模型能够反映材料的几何参数与流阻率之间的变化规律,为纤维多孔金属吸声材料的微观结构设计提供了一定的依据。

卧铺动车组床垫材料吸声特性测试及仿真优化

基于传递函数法,利用阻抗管测试卧铺动车组床垫材料的吸声特性.基于声学有限元法,用Delany-BazleyMiki经验模型模拟多孔吸声材料声学属性,建立阻抗管吸声特性计算模型,并由试验结果进行校核.基于该模型,计算分析厚度、孔隙率和流阻率对卧铺动车组床垫材料吸声特性的影响.结果表明：增加厚度会使得平均吸声系数和降噪系数增大,但当厚度超过70mm后,吸声特性变化趋于稳定,频域吸声系数主要在50~500Hz的中低频显著提高;增大孔隙率会使材料平均吸声系数和降噪系数增大,但增大幅度不大,同时可使100~800 Hz的中低频吸声系数有小幅提高;增大流阻率使得平均吸声系数和降噪系数呈先增大后减小的趋势,峰值均出现在流阻率为0.5×105 Pa·s/m2左右.优化后的材料相比于原试样,提高了100~500 Hz的吸声性能,且平均吸声系数提高了12.85%,降噪系数提高了16.69%.

金属橡胶材料双层结构吸声特性研究

理论研究了金属橡胶材料双层结构吸声特性。根据金属橡胶材料声学特性参数计算式,推导出两种基本双层吸声结构—置于刚性墙和带有空气层吸声结构的声阻抗率和吸声系数计算式。确定了流阻率是决定金属橡胶材料声学特性的基本参数。分析了各层材料厚度、流阻率及空气层厚度对两种吸声结构吸声性能的影响关系,对比分析了双层吸声结构与单层吸声结构的吸声性能。研究结果表明:通过合理设计双层吸声结构,可使其在很宽的频率范围内具有良好的吸声性能。

汽车驾驶室吸声材料的吸声系数计算方法

针对汽车驾驶室吸声材料的吸声系数的一种简便计算方法进行研究.根据吸声材料声阻抗率布置,得到吸声材料流阻率和孔隙率的计算公式,利用Matlab循环程序计算出流阻率和孔隙率,根据求得的吸声材料的流阻率和孔隙率,可以理论计算出汽车驾驶室吸声材料的吸声系数,为理论计算汽车驾驶室吸声材料的吸声系数提供一种简便方法.同时系统研究材料的吸声系数与吸声材料自身的流阻率、孔隙率和厚度以及入射声波频率的关系,在低频时吸声系数与材料的孔隙率和厚度成正比;当入射声波在0～500Hz范围内,驾驶室吸声材料的系数随流阻率的减小略有下降,但下降幅度并不显著;随着入射声波频率的提高,驾驶室吸声材料的吸声系数一般呈上升趋势.

陶粒吸声材料声学参数的试验研究

陶粒吸声材料是以陶粒为骨料,水泥为胶凝材料,添加外加剂制备而成。通过试验分析增加水灰比、置换微细陶粒、添加乳胶粉和聚丙烯纤维对陶粒吸声材料的吸声系数和流阻率的影响。结果表明:增加水灰比、置换微细陶粒、添加乳胶粉和聚丙烯纤维都会使流阻率升高,但平均吸声系数并不随着流阻率的升高而升高;混合级配下水灰比为0.20的陶粒吸声材料吸声效果更好;添加微细陶粒能提升陶粒吸声材料高频段的吸声性能;添加1.0%的乳胶粉和0.3%的聚丙烯纤维使陶粒吸声材料的吸声系数分别降低了0.02和0.01。

泡沫铝百叶窗声屏障隔声计算及验证

基于3D有限元法和隔声计算理论,将百叶窗叶片考虑成多孔吸声材料,建立开孔声屏障声学有限元隔声计算模型,并基于此模型分析泡沫铝材料属性对百叶窗声屏障隔声性能的影响。隔声计算模型通过现有理论与试验结果对比验证,理论验证不考虑泡沫铝材料,试验对比验证考虑泡沫铝材料。基于验证后的有限元隔声计算模型,调查泡沫铝材料流阻率和降噪系数对百叶窗声屏障隔声性能的影响。结果表明,声屏障计权隔声量与泡沫铝流阻率近似为线性关系,并且泡沫铝材料流阻率越小越好;声屏障计权隔声量与泡沫铝降噪系数呈指数关系,当降噪系数大于0.55时,进一步提高吸声材料的降噪系数对百叶窗声屏障隔声量影响较小。

纤维截面形状对聚酯纤维材料吸声性能的影响研究

为探讨聚酯纤维截面形状对吸声性能的影响,通过热压法制备了4种不同纤维截面形状的聚酯纤维板,利用阻抗管对4种聚酯纤维板在80~6300 Hz频率范围内的吸声性能进行测试。根据流阻率模型和声阻抗模型对材料吸声性能进行预测,并将该模型的计算结果与测试结果进行比较。结果表明:扁平截面的聚酯纤维材料的吸声性能最佳,平均吸声系数达到0.404;对于聚酯纤维材料的吸声系数与模型的计算值,圆形截面聚酯纤维材料吻合较好(全频段误差率为2.036%),异形截面聚酯纤维材料的误差较大。

Three-dimensional forward modeling of DC resistivity using the aggregation-based algebraic multigrid method

To speed up three-dimensional （3D） DC resistivity modeling, we present a new multigrid method, the aggregation-based algebraic multigrid method （AGMG）. We first discretize the differential equation of the secondary potential field with mixed boundary conditions by using a seven-point finite-difference method to obtain a large sparse system of linear equations. Then, we introduce the theory behind the pairwise aggregation algorithms for AGMG and use the conjugate-gradient method with the V-cycle AGMG preconditioner （AGMG-CG） to solve the linear equations. We use typical geoelectrical models to test the proposed AGMG-CG method and compare the results with analytical solutions and the 3DDCXH algorithm for 3D DC modeling （3DDCXH）. In addition, we apply the AGMG-CG method to different grid sizes and geoelectrical models and compare it to different iterative methods, such as ILU-BICGSTAB, ILU-GCR, and SSOR-CG. The AGMG-CG method yields nearly linearly decreasing errors, whereas the number of iterations increases slowly with increasing grid size. The AGMG-CG method is precise and converges fast, and thus can improve the computational efficiency in forward modeling of three-dimensional DC resistivity.

Finite element numerical simulation of 2.5D direct current method based on mesh refinement and recoarsement

To deal with the problem of low computational precision at the nodes near the source and satisfy the requirements for computational efficiency in inversion imaging and finite-element numerical simulations of the direct current method, we propose a new mesh refinement and recoarsement method for a two-dimensional point source. We introduce the mesh refinement and mesh recoarsement into the traditional structured mesh subdivision. By refining the horizontal grids, the singularity owing to the point source is minimized and the topography is simulated. By recoarsening the horizontal grids, the number of grid cells is reduced significantly and computational efficiency is improved. Model tests show that the proposed method solves the singularity problem and reduces the number of grid cells by 80% compared to the uniform grid refinement.

金属纤维材料的吸声特性

本文用驻波管法测试了多种规格的碳钢、黄铜、铝纤维等吸声材料的垂直入射吸声系数,频率范围为100～4000Hz;分析讨论了材料的流阻率、厚度、容量、孔隙率、纤维直径及背后空气层对其吸声性能的影响;并对模压金属纤维材料的结构因子作了探讨。

计量站变径输气管道包裹降噪仿真研究

建立计量站变径输气管道包裹降噪仿真模型,根据实测现场噪声频谱特性制作合适的声学有限元网格,运用Virtual.Lab Acoustics软件模拟变径输气管道包裹降噪效果,分析包裹结构、材料性能对降噪的影响。模拟仿真结果表明,随着包裹材料流阻率增大,降噪效果降低;包裹材料厚度增加,降噪效果增强。模拟计算结果与实测噪声吻合较好,充分证实了仿真研究方法的正确性,可为输气管道包裹降噪工艺技术的实施提供参考。

LSM95-8YSZ阴极的孔隙结构优化及性能研究

电极材料的孔隙结构是电极支撑型固体氧化物燃料电池(ES-SOFC)长期稳定运行的关键因素。采用高温固相法合成(La_(0.75)Sr_(0.25))_(0.95)MnO_(3)(LSM95)阴极粉末、物理分散的方法制备木质纤维作为造孔剂,对SOFC阴极的孔隙结构进行优化。为模拟真实电堆内的气体损耗,设计一种测试流阻率和模拟损耗的装置,并结合X射线衍射(XRD)、扫描电镜(SEM)、热膨胀仪和四电极法研究孔隙结构对阴极性能的影响。结果表明,高温固相法合成的LSM95为单钙钛矿结构且颗粒均一,LSM95与氧化钇稳定的氧化锆(8YSZ)在1250℃烧结不会相互反应。木质纤维作为造孔剂,可得到具有高孔隙率的连通孔,这种孔道结构有低的空气流阻率,并且在多次模拟损耗后,电导率只下降约3%。研究结果对ES-SOFC的电极造孔有实际指导意义。

Feasibility Research on the High Speed Rotary Positive Air Filter

The structure, separation principle and feasibility research for a new type of vehicle air filter called the high speed rotary positive air filter were described. The analysis of the experimental data showed that the principle and structure of it were feasible and it possessed high separation efficiency and great self cleaning ability. Compared with the conventional air filter it also has lower air intake loss. So it is worth further practical research.

Electrical conductivity of MO(MO=FeO,NiO)-containing CaO-MgO-SiO_2-Al_2O_3 slag with low basicity

As a fundamental study on recovery of valuable metals from nonferrous metallurgical slags,electrical conductivity values of MO（MO=FeO,NiO）-containing CaO-MgO-SiO2-Al2O3 slag with a low basicity were measured at different temperatures using AC impedance spectroscopy.The result shows that the electrical conductivity increased from 1.4 S/m to 14.4 S/m with the increase of the temperature from 1 573 to 1 773 K and the content of MO which is less than 12% under the constant mass ratio of （CaO＋MgO） to （SiO2＋Al2O3） of 0.47.Moreover,the increase magnitude of the electrical conductivity was also promoted with the increase of the content of MO.The electrical conductivity of FeO-containing slags was close to that of NiO-containing slags when the content was less than 8%;however,it was obviously larger than that of NiO-containing slags when the content was 12%.The activation energy of the electrical conductivity decreased with the increase of MO content.

3-D direct current resistivity forward modeling by adaptive multigrid finite element method

Based on the fact that 3-D model discretization by artificial could not always be successfully implemented especially for large-scaled problems when high accuracy and efficiency were required, a new adaptive multigrid finite element method was proposed. In this algorithm, a-posteriori error estimator was employed to generate adaptively refined mesh on a given initial mesh. On these iterative meshes, V-cycle based multigrid method was adopted to fast solve each linear equation with each initial iterative term interpolated from last mesh. With this error estimator, the unknowns were nearly optimally distributed on the final mesh which guaranteed the accuracy. The numerical results show that the multigrid solver is faster and more stable compared with ICCG solver. Meanwhile, the numerical results obtained from the final model discretization approximate the analytical solutions with maximal relative errors less than 1%, which remarkably validates this algorithm.

Numerical modeling of anisotropy paradoxes in direct current resistivity and time-domain induced polarization methods

Based on an analytical solution for the current point source in an anisotropic half-space,we study the apparent resistivity and apparent chargeability of a transversely isotropic medium with vertical and horizontal axes symmetry,respectively.We then provide a simple derivation of the anisotropy paradoxes in direct current resistivity and time-domain induced polarization methods.Analogous to the mean resistivity,we propose a formulation for deriving the mean polarizability.We also present a three-dimensional finite element algorithm for modeling the direct current resistivity and time-domain induced polarization using an unstructured tetrahedral grid.Finally,we provide the apparent resistivity and apparent chargeability curves of a tilted,transversely isotropic medium with diff erent angles,respectively.The subsequent results illustrate the anisotropy paradoxes of direct current resistivity and time-domain induced polarization.

Multiple linear system techniques for 3D finite element method modeling of direct current resistivity

The strategies that minimize the overall solution time of multiple linear systems in 3D finite element method (FEM) modeling of direct current (DC) resistivity were discussed. A global stiff matrix is assembled and stored in two parts separately. One part is associated with the volume integral and the other is associated with the subsurface boundary integral. The equivalent multiple linear systems with closer right-hand sides than the original systems were constructed. A recycling Krylov subspace technique was employed to solve the multiple linear systems. The solution of the seed system was used as an initial guess for the subsequent systems. The results of two numerical experiments show that the improved algorithm reduces the iterations and CPU time by almost 50%, compared with the classical preconditioned conjugate gradient method.

Forward modeling for “earth-ionosphere” mode electromagnetic field

A fixed artificial source(greater than 200 kW) was used and the source location was selected at a high resistivity region to ensure high emission efficiency. Some publications used the "earth-ionosphere" mode in modeling the electromagnetic(EM) fields with the offset up to a thousand kilometer, and such EM fields still have a signal/noise ratio of 10-20 dB. This means that a new EM method with fixed source is feasible, but in their calculation, the displacement in air was neglected. In this work, some three-layer modeling results were presented to illustrate the basic EM fields' characteristics in the near, far and waveguide areas under "earth-ionosphere" mode, and a standard is given to distinguish the boundary of near, far and waveguide areas. Due to the influence of the ionosphere and displacement current in the air, the "earth-ionosphere" mode EM fields have an extra waveguide zone, where the fields' behavior is very different from that of the far field zone.

Influence of soil resistivity on stray current in power supply system of urban rail transit

In order to explore the influence of soil resistivity on stray current in power supply system of urban rail transit,we establish an equivalent circuit model of the rail-to-ground structure based on resistance network method first.After measuring the soil resistivity of a real subway system,a simulation model is established in Matlab to obtain the stray currents at different soil resistivities.Then the influence of soil resistivity on stray current is analyzed.Afterwards,to verify the rationality and reliability of the simulation model,we design a test circuit to measure the stray current and rail-to-ground voltage in a real subway system,and a comparison of the experimentally measured results and simulation results is presented.The results show that the stray current is the maximum when the soil resistivity is 211.57Ω·m;when the soil resistivity is 768.47Ω·m,the stray current is the minimum,that is,the smaller the soil resistivity,the greater the stray current.Therefore,the resistivity should be increased as much as possible when ramming the track foundation in urban rail transit system.