Time effect and prediction of broken rock bulking coefficient on the base of particle discrete element method

Bulking characteristics of gangue are of great significance for the stability of goafs in mining overburden in the caving zones.In this paper,a particle discrete element method with clusters to represent gangue was adopted to explore the bulking coefficient time effect of the broken rock in the caving zone under three-dimensional triaxial compression condition.The phenomena of stress corrosion,deformation,and failure of rock blocks were simulated in the numerical model.Meanwhile,a new criterion of rock fragments damage was put forward.It was found that the broken rock has obvious viscoelastic properties.A new equation based on the Burgers creep model was proposed to predict the bulking coefficient of broken rock.A deformation characteristic parameter of the prediction equation was analyzed,which can be set as a fixed value in the mid-and long-term prediction of the bulking coefficient.There are quadratic function relationships between the deformation characteristic parameter value and Talbot gradation index,axial pressure and confining pressure.

TESTING FOR VARYING DISPERSION IN DISCRETE EXPONENTIAL FAMILY NONLINEAR MODELS

It is necessary to test for varying dispersion in generalized nonlinear models.Wei,et al(1998) developed a likelihood ratio test,a score test and their adjustments to test for varying dispersion in continuous exponential family nonlinear models.This type of problem in the framework of general discrete exponential family nonlinear models is discussed.Two types of varying dispersion,which are random coefficients model and random effects model,are proposed,and corresponding score test statistics are constructed and expressed in simple,easy to use,matrix formulas.

Discrete wavelet and modified PCA decompositions for postural stability analysis in biometric applications

The aim of this study is to compare the Discrete wavelet decomposition and the modified Principal Analysis Component (PCA) decomposition to analyze the stabilogram for the purpose to provide a new insight about human postural stability. Discrete wavelet analysis is used to decompose the stabilogram into several timescale components (i.e. detail wavelet coefficients and approximation wavelet coefficients). Whereas, the modified PCA decomposition is applied to decompose the stabilogram into three components, namely: trend, rambling and trembling. Based on the modified PCA analysis, the trace of analytic trembling and rambling in the complex plan highlights a unique rotation center. The same property is found when considering the detail wavelet coefficients. Based on this property, the area of the circle in which 95% of the trace’s data points are located, is extracted to provide important information about the postural equilibrium status of healthy subjects (average age 31 ± 11 years). Based on experimental results, this parameter seems to be a valuable parameter in order to highlight the effect of visual entries, stabilogram direction, gender and age on the postural stability. Obtained results show also that wavelets and the modified PCA decomposition can discriminate the subjects by gender which is particularly interesting in biometric applications and human stability simulation. Moreover, both techniques highlight the fact that male are less stable than female and the fact that there is no correlation between human stability and his age (under 60).

Continuous and Discrete Similarity Coefficient for Identifying Essential Proteins Using Gene Expression Data

Essential proteins play a vital role in biological processes,and the combination of gene expression profiles with Protein-Protein Interaction(PPI)networks can improve the identification of essential proteins.However,gene expression data are prone to significant fluctuations due to noise interference in topological networks.In this work,we discretized gene expression data and used the discrete similarities of the gene expression spectrum to eliminate noise fluctuation.We then proposed the Pearson Jaccard coefficient(PJC)that consisted of continuous and discrete similarities in the gene expression data.Using the graph theory as the basis,we fused the newly proposed similarity coefficient with the existing network topology prediction algorithm at each protein node to recognize essential proteins.This strategy exhibited a high recognition rate and good specificity.We validated the new similarity coefficient PJC on PPI datasets of Krogan,Gavin,and DIP of yeast species and evaluated the results by receiver operating characteristic analysis,jackknife analysis,top analysis,and accuracy analysis.Compared with that of node-based network topology centrality and fusion biological information centrality methods,the new similarity coefficient PJC showed a significantly improved prediction performance for essential proteins in DC,IC,Eigenvector centrality,subgraph centrality,betweenness centrality,closeness centrality,NC,PeC,and WDC.We also compared the PJC coefficient with other methods using the NF-PIN algorithm,which predicts proteins by constructing active PPI networks through dynamic gene expression.The experimental results proved that our newly proposed similarity coefficient PJC has superior advantages in predicting essential proteins.

Approximation of Derivative for a Singularly Perturbed Second-Order ODE of Robin Type with Discontinuous Convection Coefficient and Source Term

In this paper, a singularly perturbed Robin type boundary value problem for second-order ordinary differential equation with discontinuous convection coefficient and source term is considered. A robust-layer-resolving numerical method is proposed. An e-uniform global error estimate for the numerical solution and also to the numerical derivative are established. Numerical results are presented, which are in agreement with the theoretical predictions.

Generalized Algorithms of Discrete Optimization and Their Power Engineering Applications

Generalized algorithms for solving problems of discrete, integer, and Boolean programming are discussed. These algorithms are associated with the method of normalized functions and are based on a combination of formal and heuristic procedures. This allows one to obtain quasi-optimal solutions after a small number of steps, overcoming the NP-completeness of discrete optimization problems. Questions of constructing so-called “duplicate” algorithms are considered to improve the quality of discrete problem solutions. An approach to solving discrete problems with fuzzy coefficients in objective functions and constraints on the basis of modifying the generalized algorithms is considered. Questions of applying the generalized algorithms to solve multicriteria discrete problems are also discussed. The results of the paper are of a universal character and can be applied to the design, planning, operation, and control of systems and processes of different purposes. The results of the paper are already being used to solve power engineering problems.

基于改进切尾均值的矿井图像去噪算法

现有矿井图像去噪算法对于复杂噪声的去除效果有限,且处理速度不能满足实时监控需求。针对该问题,提出一种基于改进切尾均值的矿井图像去噪算法。首先,采用切尾均值滤波器对图像噪声进行初步滤除,同时引入二次检验机制处理残留的噪声点,通过引入离散系数提升算法对不同像素的区分能力,增强去噪性能;其次,采用基于极值数量的分类处理及再次检验机制,有效减少残留噪声问题;然后,在小波函数中引入新的控制变量优化软阈值函数和硬阈值函数,构建双阈值函数,结合Radon变换增强对线性特征的处理,增强对矿井图像的检测能力;最后,采用均方误差(MSE)与峰值信噪比(PSNR)进行图像质量评价。实验结果表明:相较于切尾均值算法、硬阈值算法、软阈值算法,基于改进切尾均值的矿井图像去噪算法处理的图像的MSE增长相对缓慢,MSE最小,图像去噪效果最好;引入离散系数后,去噪图像的MSE相较于引入前低300 dB左右,PSNR相较于引入前高20 dB左右,引入离散系数能有效减少噪声点对算法的影响;相较于卡尔曼遗传优化算法、变换域图像去噪算法、交叉分支卷积去噪网络,基于改进切尾均值的矿井图像去噪算法处理的图像MSE分别降低了27,21,13 dB,PSNR分别提升了8,6,3 dB,去噪耗时分别缩短了0.20,0.16,0.14 s。

基于频谱拆分的高比例新能源电力系统火电-多类型储能容量优化匹配

“双碳”背景下的新型电力系统可再生能源接入比例持续增大,火电装机保留量将逐步降低,源荷平衡将由抽水蓄能、电化学储能等多类型储能配合火电共同完成。该文提出在已知目标年新能源装机与负荷容量下对火电与多类型储能容量需求的评估方法。首先对净负荷时间序列做离散傅里叶变换(discrete Fourier transform,DFT),将所得频谱进行聚类,并引入连续变量分布系数将单一频率分量能同时分配给火电机组、抽水储能和电池储能,从而进行傅里叶反变换得到时域调度曲线,评估或优化火电和多类型储能容量。该文所提容量匹配优化的目标函数是凸函数,由于采用了连续变量分布系数,约束条件是线性等式和不等式,整个问题可以转化为线性规划求解,克服了基于截止频率法难以充分利用火电灵活性的局限性和计算模型的非凸性。参考西北电网数据构建场景并进行算例分析,验证了所提模型能够充分利用火电调节潜力,协调火-储联合运行。比较不同风光比例下和不同新能源接入规模的匹配结果,表明适当的风光比和接入规模有助于降低总体投资成本。

不同粗骨料粒径混凝土动态压缩强度的离散性研究

为了研究粗骨料粒径差异引起的动态压缩试验离散性问题,制备了最大粒径分别为8 mm、14 mm和26 mm的混凝土与砂浆试件,通过动静态压缩试验,得到不同应变率下各试样的应力-应变曲线和应变率-动态增长因子曲线。为了更直观地分析由粗骨料粒径差异引起的试验离散性问题,定义粒径系数λ为粗骨料最大粒径d与试件直径D之比,引入变异系数CV,运用数理统计方法量化离散性,得到λ与CV关系图,直观反映试验离散性与粗骨料粒径关系。分析表明:λ=0.34为混凝土材料异质性临界点;当粒径系数λ<0.34时,混凝土材料异质性影响不明显;当λ>0.34时,粗骨料的粒径过大已经影响到了混凝土的动态响应,材料异质性明显增强。该结论的得出对今后工程与试验中粗骨料粒径的选取有指导意义。

基于蓄热式固定床气化装置的木质生物质固废气化CFD模拟

基于计算流体力学-稠密离散相模型,建立新型蓄热式气化装置的数值模拟模型,根据上吸式固定床气化特性优化了前处理设置,研究不同过量空气系数下炉内流体流速、压力、温度与组分的分布,分析炉内各组分质量分数在不同时刻及过量空气系数下的分布及演化规律。研究表明,颗粒床层为影响流体流速、压降的主要因素,流体流经床层产生了50~75 Pa的压降。炉内温度场呈现出明显的干燥-热解-还原氧化分区,各工况的温度曲线几乎重叠,大致存在4个拐点。在低过量空气系数区间,气化剂流率的提升对燃气组分影响不大。气化装置的设计有利于提升燃气中H2的质量分数及CO/CO_(2)的质量分数之比,有效提升了燃气热值。

JPEG量化步长估计综述

随着JPEG(Joint Photographic Experts Group)格式的图片在网络存储和传输中的广泛应用,基于JPEG格式的篡改、拼接等恶意操作也层出不穷,利用JPEG图像特性的研究受到越来越多的关注。其中,JPEG图像特性与量化步长息息相关。如果,JPEG压缩后的图像以位图的形式进行保存,研究者无法直接获取到量化步长,从而无法有效地分析JPEG图像特性。因此,对于量化步长的估计在数字图像取证领域越来越受到关注。本文首先介绍了量化步长估计的研究背景,并将量化步长估计问题分成两类问题:单压缩图像的量化步长估计和重压缩图像的首次量化步长估计。其次,在经典的JPEG压缩模型基础上分别了给出了这两类问题的量化步长估计模型,并对每类问题的各种现有方法进行了详细介绍和梳理。随后,在相同实验环境下对经典算法进行了实验,并对经典算法进行了相应的分析与评价。实验结果表明:在单压缩图像的量化步长估计任务中,现有技术相对成熟并且部分算法估计准确率高于90%;但是,在对齐重压缩图像的首次量化步长估计任务中,现有方法仅能估计低频、中频的量化步长,并且当首次与第二次的压缩质量因子相近时,估计准确率较低;在非对齐重压缩图像的首次量化步长估计任务中,由于网格偏移会增加估计量化步长的困难,导致算法在非对齐重压缩上性能较差。最后,指出了量化步长估计中有待进一步解决的问题和发展趋势。

转轮式日粮混合机叶板结构优化设计

试验旨在对有效容积为0.5 m^(3)的转轮式日粮混合机的叶板结构进行优化设计,以提高其混合均匀性。利用Solid works软件建立整机模型,通过改变搅拌架叶板形状的方式进行优化设计,分别将优化前后的模型导入ANSYS软件进行有限元分析和利用EDEM软件进行离散元仿真分析;并搭建台架试验,通过叶板所承受最大转矩及离散系数两个评价指标来验证优化的可行性。有限元分析结果表明:叶板形状优化后最大应力较优化前下降40.38%;最大结点位移较优化前下降40.42%;对优化前后的转轮式日粮混合机进行离散元仿真,计算优化前后的离散系数。从整体数据上看,优化后结构的离散系数较小,即优化后日粮混合机的混合均匀度更高,且进行台架试验得出的结果符合上述分析。得出优化后结构的刚度和混合均匀性均优于优化前,验证了结构优化的可靠性。

聚丙烯纤维加固土融沉特性的离散元数值模拟研究

针对掺入纤维对土体冻融特性的影响进行离散元数值模拟,首先自研了过程感知融化固结系统,基于融沉试验,提出了微观参数折减法模拟融化过程,分析了纤维掺量、纤维长度、土样高度的影响规律。结果表明:离散元方法可对融沉过程进行较为有效的模拟,并可得到最优纤维掺量,对于模拟工况,最优纤维掺量为0.1%;从融化压缩模量看,纤维长度与掺量为敏感影响因素,土样高度为次要因素;掺入纤维对土体强度与融沉特性的提升效果具有一致性。

仔猪拨片式饲喂装置排料单元优化设计

为了解决规模化仔猪饲喂过程中出现的饲料浪费和饲喂装置排料不均匀等问题,试验设计了一种仔猪拨片式饲喂装置的排料单元(包括饲料挡板、套筒和排料拨片)并对其结构参数进行了优化;以分散度为指标评价了采用直线型、曲线型、前曲后直型排料拨片的饲喂装置的排料性能,筛选出最佳排料拨片形状;在最佳排料拨片形状下,以排料拨片转速、套筒半径及排料拨片叶数为因素,以流量(指饲喂装置的排料速率)和离散系数(指饲喂装置的排料均匀性)为指标分析排料单元最佳结构参数组合。结果表明:排料单元中饲料挡板设计为直径160 mm、厚度为4 mm的圆盘,且排料拨片采用前曲后直型更有助于提高饲喂装置的排料速率和排料均匀性;当排料拨片转速为62 r/min、套筒半径为91.4 mm、排料拨片叶数为4叶时饲喂装置的排料性能最优,此时流量和离散系数分别为158.65 g/s和4.26%。说明优化后的仔猪饲喂装置的排料单元有效实现了均匀排料且排料速率较高。

基于EDEM的土荆芥茎秆离散元参数标定

针对目前土荆芥植物收获设备研发中离散元仿真缺乏准确模型问题。以土荆芥茎秆为研究对象,在离散元EDEM软件中对物理和粘结参数进行标定。为测定土荆芥茎秆的泊松比、剪切模量、碰撞恢复系数、静摩擦系数、滚动摩擦系数等物理参数和切向接触刚度、临界法向应力、临界切向应力、粘结半径等粘结参数,以休止角和剪切试验为基础,采用Plackett-Burman、Steepest ascent和Box-Behnken试验进行休止角仿真研究,测定土荆芥的物理参数。仿真休止角与物理休止角相对误差为0.47%;以确定的粘结参数进行剪切仿真试验;仿真剪切破坏力与物理试验破坏力相对误差为0.84%。所标定的参数能够真实反映土荆芥茎秆的力学特性,结果为土荆芥收获机械研发中离散元仿真提供理论支撑。

带柔性部件飞行器刚性耦合系数矩阵优化算法

针对目前飞行器刚性耦合系数矩阵算法中按照单元节点规律排列的质量矩阵数据处理难度大,运算维度高的问题,本文提出一种非离散化方法的刚性耦合系数矩阵优化算法,利用在三维模型中可以直接获取的柔性部件质量特性,替代高维度的质量矩阵参与计算,避免了模型离散化误差,在简化刚性耦合系数计算流程的同时,具有提高计算结果准确度的效果,增强了工程设计中的便利性.

坡顶车辆荷载作用下顺向泥岩边坡破坏机理分析

基于贵州某高速公路顺向泥岩边坡,将坡顶车辆荷载考虑为均布静载,采用离散元UDEC软件,研究坡顶荷载大小及作用位置对顺向泥岩边坡变形破坏机理的影响。结果表明:边坡上部岩体先沿层面产生顺层滑移,边坡破坏模式为推移式滑坡;随着坡顶车辆荷载的增加,边坡的稳定性系数不断降低,最大位移不断增大,但边坡潜在滑面位置及变形失稳范围基本不变;随着坡顶荷载距坡肩的距离增大,边坡的稳定系数不断增大,最大位移量不断减小,但潜在滑面后缘不断后移,潜在失稳范围增大。

基于DEM的导种管优化设计方法研究

为提高玉米精量播种机播种均匀性,需要合理的导种管引导种子进入种沟,基于离散元法研究玉米精量播种机导种管的优化设计。以零速投种理论为基础,采用运动学能量守恒方程分析导种管主曲线,得到种子在导种管出口处的水平速度方程;基于Isight软件RSM优化模块设计试验,结合所得导种管出口处水平速度方程,以圆弧段夹角α、直线段与竖直方向夹角β、直线段高度h1、圆弧段半径R为因素,考虑分析出口水平速度及实际农艺种子株距的范围调节,增加排种盘角速度ω为因素,以株距变异系数、出口水平速度为响应设计试验对主曲线参数进行优化求解。在ω为15~45 r/min参数范围下,以出口水平速度小于0.1 m/s,变异系数小于5%进行寻优求解,得到导种管主曲线的最佳参数组合为:α=25°,β=11°,h_(1)=200 mm,R=625 mm。根据所得最佳参数采用CATIA软件建立三维模型并3D打印进行台架试验,台架试验所得种子变异系数为11.58%、合格指数为98.2%、漏播指数为0.83%、重播指数为0.97%,结果表明导种管主曲线优化设计合理。

基于开沟施肥的撒肥圆盘设计与试验

针对传统果树开沟施肥机存在的肥料分布不均问题,设计了一种基于开沟施肥的撒肥圆盘。首先,建立撒肥圆盘的三维模型,对肥料颗粒在撒肥圆盘上的受力和运动进行分析,建立肥料颗粒的运动方程;通过离散元软件建立仿真模型,以撒肥圆盘的盘面倾角、母线极角、肥盘转速为试验因素,以肥料分布均匀性变异系数、施肥量偏差为实验指标,开展二次旋转正交组合试验。对撒肥圆盘的施肥效果进行仿真分析,结果表明:颗粒肥料在盘面倾角为0°、母线极角为120°、肥盘转速为72r/min时,肥料分布均匀性变异系数为14.42%,施肥质量偏差为4.50%,肥料分布均匀性较好,能够满足果树施肥的要求,可为撒肥圆盘在开沟施肥中的应用提供理论参考。

非轴对称外荷载条件下深埋隧洞变形特征研究

为研究非轴对称外荷载条件的地下典型隧洞变形特征,基于圆形隧洞、非圆形隧洞的解析解,总结了洞壁应力、位移的影响因子;采用数值模拟,建立变侧压系数下三种非圆形隧洞离散元模型,得到隧洞岩体的应力、位移、破裂分布模式。研究结果表明:对于圆形隧洞,洞壁上应力差最大,最易发生破坏;总应力集中系数变化特征为变量侧压系数的单调函数;径向位移对围岩稳定性起主导作用。对于非圆形隧洞,侧压系数的增大,围岩的主导位移由垂直位移转变为水平位移;侧压系数从0.5→1.0→2.0变化时,最大主应力由边墙转移至拱顶,最小主应力始终集中在边墙洞周;同外荷载、同侧压系数时,城门洞隧洞围岩破坏形式简单,塑性区半径小,矩形隧洞围岩破坏形式复杂,塑性区半径大,椭圆形隧洞在侧压系数小于1时边墙塑性区半径最大。