基于有限元方法的木材含水率和密度空间分布模型

针对木材特点,用控制体积有限元方法对板材模型进行网格划分,采用有限元方法将数学方程离散化,建立了木材含水率和密度空间分布的数学模型。根据数学模型建立了木材含水率和密度空间分布的三维仿真图,验证了模型的准确性。

木材快速生长期内早材与晚材密度分布的数学描述初探

对树木生长及早晚材密度的分布规律进行理论研究。首先,利用正弦波函数与分段线性函数分别模拟环境温度与降雨量随年份的周期性变化规律。其次,在分析环境温度与降雨量对树木生长速率影响的基础上,建立以生长时间为自变量、以树干半径为因变量的树木生长速率模型;在分析树木生长速率对木材早晚材的形成及其密度分布影响的基础上,构建早晚材密度分布模型。最后,以人工林杉木为例,一方面,利用有限差分法分别求解树木生长速率模型与早晚材密度分布模型;另一方面,采用软X射线密度分析仪测定木材径向的密度分布值,将密度的试验测量值与模型计算值进行比较,对早晚材密度分布模型进行验证。结果表明:1)可采用正弦波函数量化树木生长环境中温度的周期性变化,函数拟合的决定系数为0.907;树木生长环境中的降雨量周期性变化可用分段线性函数定量描述;2)树木生长速率模型可以定量分析温度与降雨量对树木生长的影响;3)早晚材密度分布模型可准确描述木材快速生长期内的早晚材密度沿径向的分布规律,为木材宏观密度与微观密度的内在联系给出定量的表述。

基于模型的检泵周期预测

检泵周期是机械采油中一项重要的综合性经济技术指标,油田开采管理工作已把检泵周期作为一项重要考核内容,通过检泵周期来评价技术管理和生产管理的水平。本文通过对检泵周期进行统计寻找其中的规律,建立了检泵周期概率密度分布模型和可靠性预测模型。通过仿真分析实例,对建立模型进行可靠性验证,通过作业某队工艺队提供的近年来采油某厂检泵的统计数据,验证了本文建立模型的可靠度,最终发现可靠度预测模型的预测精度取决于样本大小,增大样本可以提高预测精度。检泵的周期的预测可以更好地考核采油矿的生产,以及作业某队的作业质量。

导弹再入过程中电磁波传输的研究

阐述了在导弹再入过程中,电磁波在等离子体鞘套中的传播特性.针对导弹前端的等离子体鞘套中电子密度分布模型,以及等离子体鞘套中的电子密度、碰撞频率和电磁波的入射角度还有温度、压强等因素对电磁波的反射、透射和吸收的影响进行了讨论,得到了电磁波在等离子体鞘套中传输特性与各因素之间的关系图象.如果要解决导弹再入过程中出现的通讯中断问题,就需要建立电子密度分布模型、温度与电子密度、温度与碰撞频率的函数模型等.

Q345E钢焊接热影响区相变的计算机模拟

以Kirkaldy和Koistinen-Marburger相变模型为基础,建立焊接热影响区相变模型。以Q345E钢平板对接焊为例,用Goldak双椭球功率密度分布热源模型计算焊接热循环,用ABAQUS有限元分析软件对焊接过程中的热影响区的相变进行数值模拟。以相同焊接规范进行焊接试验,利用Image-pro-plus软件进行组织测定。将试验结果与模拟结果进行比较分析,二者吻合良好,证明本焊热影响区相变模型可以准确分析焊接热影响区相变情况,对优化焊接工艺参数、改善焊接接头性能、提高焊接产品质量具有重要指导作用。

基于随机抽样一致性算法的运动标定方法

在邦定设备运动标定过程中收集到的对位平台旋转中心的样本数据包含有各种干扰,以至于利用其进行推导时过程复杂、结果精度低且鲁棒性不高。为了解决以上问题,提出一种基于随机抽样一致性算法的简单方法,该方法的构建基于样本数据分布密度模型,该模型进行一定次数的迭代筛选后,其最优解集合可进行精确推导。试验表明,在使用随机选取的10组样本数据的计算中,本方法平均计算时间为697.6s,标定精度在7.2pixel以内,并且有7组数据的结果均满足10pixel的像素精度要求。整个标定结果达到国外同类型设备的先进水平,能够完全满足设备运行的要求。

基于机器学习的云存储数据分段聚类方法仿真

针对传统的云存储数据分段聚类方法存在运行效率较低、聚类结果不够平滑等问题,提出一种基于机器学习的云存储数据分段聚类方法。从云存储数据库中合理抽取多个小数据集,小数据集包含云存储数据库中的所有自然簇,根据相似度定义构建相似度矩阵。采用非线性核主成分算法实现对相似度矩阵中数据相似度的测度,通过相似度测度将具有相同特征的数据归为一类,采用混合高斯分布概率密度模型计算不同类别数据的后验概率,通过对概率大小的比较实现云存储数据分段聚类。实验结果证明,所提方法能够缩短聚类运行时间,将聚类变化度降低到29%,有效提高了聚类结果的平滑度。

利用引力场的高斯定理推算地球内部压强

利用静电场与万有引力场规律的相似性,建立引力场高斯定理的概念,来类比得到静态万有引力场的高斯定理表达式,并将地球近似看成是质量分布具有球对称性的天体,根据布伦地球密度分布模型,运用Mathematica拟合推算出地球内部的压强,为地球的内部压强的研究提供了一种全新的思路和方法,对误差产生的来源也做了相关分析和探讨.

一种低信噪比下的有噪独立分量分析算法

针对目前大多数独立分量分析(independent component analysis,ICA)算法无噪或者弱噪声假设的局限性,提出一种适用于低信噪比情况的有噪独立分量分析算法。该算法以分离信号的负熵为目标函数,采用高斯分布密度模型作为非线性函数来估计负熵,并建立了模型参数的确定准则,能够较好地抑制低信噪比下噪声的影响,最后采用人工蜂群算法对混合矩阵进行全局寻优。仿真结果表明,与其他算法相比,提出的算法可以更为精确地估计混合矩阵,能够较好地解决低信噪比下的有噪ICA问题。

Electric field distribution in 75 kA drained aluminum reduction cell

Current distribution in a drained aluminum reduction cell is critical due to its influence on the current efficiency, electrolysis stability, anodes and cathodes integrity. A finite element model was developed to simulate the electric field in a 75 kA drained aluminum reduction cell. The current distribution and influences of the cathode inclination angle and anode-cathode distance (ACD) were studied. The results show that relatively large horizontal current density appears in the aluminum film, and the maximum value reaches 600 kA/m2. As the cathode inclination angle increases from 2° to 15°, the maximum current density of the metal pad increases by 15%, while the maximum current density of the aluminum-wettable coating layer decreases by 27%. The influence of the ACD on the current distribution is not obvious.

Traffic Flow States in a Freeway with Bottleneck

The system of mixture of single lane and double lane is studied by a cellular automata model, which is developed by us based on the Nagel and Schreckenberg＇s models. We justify that the model can reach a stable states quickly. The density distributions of the stable state is presented for several cases, which illustrate the manner of the congestion. The relationship between the outflow rate and the total number of vehicles and that between the outflow rate and the density just before the bottleneck are both given. Comparing with the relationship that occurring in the granular flow, we conclude that the transition from the free traffic flow to the congested traffic flow can also be attributed to the abrupt variation through unstable flow state, which can naturally explain the discontinuities and the complex time variation behavior observed in the traffic flow experiments.

Probabilistic total transfer capability analysis based on static voltage stability region integrated with a modified distributed-level nodal-loading model

In this paper, a new evaluation method of probabilistic TTC based on SVSR calculation is developed through a hierarchical simulation. A smooth technology based on the non-parametric kernel estimator is adapted to obtain the time-dependent probabilistic density function of the feeder-head load data. In order to describe possible operating change directions of the operating point, the original hyper-cone-like(HCL) model is constructed to consider the probabilistic distribution function(PDF) extracted from feeder-head load data to replace the simple Normal Distribution model and the uncertain generator outputs. To realize the fast TTC calculation of the current operating point in random conditions, a sub-hyper-cone-like(SHCL) model in full power injections space is proposed, which is a similarity transformation of the original one.

Nonlinear magnetic network models for flux-switching permanent magnet machines

In this paper, firstly, a basic nonlinear magnetic network model considering iron saturations is proposed for a three-phase 12-stator-slot/10-rotor-pole flux-switching permanent magnet(FSPM) machine. This model is built under cylindrical coordinates and enables the open-circuit air-gap flux-density distributions, phase permanent magnet(PM) flux-linkage, and electromotive-force(EMF) to be predicted with acceptable accuracy. However, large discrepancies are found in the predictions of armature inductances. Then, the basic model is modified by taking into account the localized saturation effect. As a result, the electromagnetic performance can be predicted more accurately, especially for the air-gap flux-density distributions. Furthermore, two improved models are proposed by adding bypass-bridge branches in stator network, to enhance the calculating accuracy of both saturated and unsaturated armature inductances. Finally, the predicted results from the four magnetic network models are validated by both 2D finite element analysis(FEA) and experimental measurements on a machine prototype. Overall, comparisons indicate that the model with bypass-bridge branches between stator teeth and back irons exhibits best performances.

Carbon turnover times shape topsoil carbon difference between Tibetan Plateau and Arctic tundra

The Tibetan Plateau(TP)and Arctic permafrost constitute two large reservoirs of organic carbon,but processes which control carbon accumulation within the surface soil layer of these areas would differ due to the interplay of climate,soil and vegetation type.Here,we synthesized currently available soil carbon data to show that mean organic carbon density in the topsoil(0-10 cm)in TP grassland(3.12±0.52 kg C m^(-2))is less than half of that in Arctic tundra(6.70±1.94 kg C m^(-2)).Such difference is primarily attributed to their difference in radiocarbon-inferred soil carbon turnover times(547 years for TP grassland versus 1609 years for Arctic tundra)rather than to their marginal difference in topsoil carbon inputs.Our findings highlight the importance of improving regional-specific soil carbon turnover and its controlling mechanisms across permafrost affected zones in ecosystem models to fully represent carbon-climate feedback.

The effect of surface roughness on thermal-elasto-hydrodynamic model of contact mechanical seals

In this paper, the effect of surface roughness on sealing clearance, pressure distribution, friction torque and leakage is studied by the thermal-elasto-hydrodynamic mixed lubrication model. A convergent nominal clearance is formed by the pressure de- formation and thermal deformation of the seal faces. This causes more serious wear in the inner side than that of the outer side of the contact area. Mass leakage increases with the growing of the surface roughness. The temperature and thermal defor- mation on the seal surface increases substantially if the roughness is reduced. The contact mechanical seals have consistent performance when the standard deviation of surface roughness is approximately 0.2 pm. In order to validate the theoretical analysis model, a method combining the measurement of three-dimensioned profile and Raman spectrum is proposed.

Model for increased efficiency of CIGS solar cells by a stepped distribution of carrier density and Ga in the absorber layer

In this paper, several structures for multilayer Cu(In1-xGax) Se2 (CIGS) thin film solar cells are proposed to achieve high conversion efficiency. All of the modeling and simulations were based on the actual data of experimentally produced CIGS cells reported in the literature. In standard CIGS cells with a single absorber layer, the effects of acceptor density and Ga content on device performance were studied, and then optimized for maximum conversion efficiency. The same procedure was performed for cells with two and three sectioned CIGS absorber layers in which Cu and/or Ga contents were varied within each consecutive section. This produces an internal additional electric field within the absorber layer, which resulted in an increase in carrier collection for longer wavelength photons, and hence, improvement in the conversion efficiency of the cell. An increase of approximately 3% in efficiency is predicted for cells with two layer absorbers. For multilayer cells in which Cu and Ga distribution were stepped simultaneously, the improvement could be approximately 3.5%. This improvement is due to; enhanced carrier collection for longer-wavelength photons, and reduced recombination at the heterojunction and back regions of the cell. These results are confirmed by the physics of the cells.

Reanalysis of Elastic Scattering of ~6Li + ^(209)Bi Reaction Using a New DensityDistribution of ~6Li Nucleus

In the present paper, the elastic scattering of6 Li + 209 Bi system is reanalyzed by using the double folding model (DFM) at energies near the Coulomb barrier (ELab=29.9 and 32.8 MeV). With this goal, a new density distribution of6 Li nucleus, the no-core full configuration (NCFC) density distribution (DD), is used to obtain the real potentials in DFM calculations. The NCFC DD results are compared with the results of both gaussian shape (GS) DD and an earlier study as well as the experimental data. This comparison provides information about the similarities and differences of the models used in calculations.

Effects of Horizontal Density Distribution on Internal Bond Strength of Flakeboard

Horizontal density variation is a structural phenomenon of non-veneer wood composites. The variation and distribution characteristics of horizontal density have impacts on the products properties. In this study, veneer strip simulated flake boards with 4 kinds of density distribution were made using a mat model. The density variation of the modeled mats was discussed, as well as the relationship between sample size and density variation. The effects of density and density distribution of non-veneer composites on the internal bond strength were analyzed. Result shows that the horizontal density of random formed particleboard follows normal distribution. Density has remarkable influence on internal bond strength (IB). Increasing density helps to improve IB at lower density stage, but has negative impacts on IB at higher density stage. Density variation between testing specimens depends on their sizes. Properly increasing specimen size can decrease the variation of the IBs.