Stability evaluation method of large cross-section tunnel considering modification of thickness-span ratio in mechanized operation

Purpose-This study aims to research the large cross-section tunnel stability evaluation method corrected after considering the thickness-span ratio.Design/methodology/approach-First,taking the Liuyuan Tunnel of Huanggang-Huangmei High-Speed Railway as an example and taking deflection of the third principal stress of the surrounding rock at a vault after tunnel excavation as the criterion,the critical buried depth of the large section tunnel was determined.Then,the strength reduction method was employed to calculate the tunnel safety factor under different rock classes and thickness-span ratios,and mathematical statistics was conducted to identify the relationships of the tunnel safety factor with the thickness-span ratio and the basic quality(BQ)index of the rock for different rock classes.Finally,the influences of thickness-span ratio,groundwater,initial stress of rock and structural attitude factors were considered to obtain the corrected BQ,based on which the stability of a large cross-section tunnel with a depth of more than 100 m during mechanized operation was analyzed.This evaluation method was then applied to Liuyuan Tunnel and Cimushan No.2 Tunnel of Chongqing Urban Expressway for verification.Findings-This study shows that under different rock classes,the tunnel safety factor is a strict power function of the thickness-span ratio,while a linear function of the BQ to some extent.It is more suitable to use the corrected BQ as a quantitative index to evaluate tunnel stability according to the actual conditions of the site.Originality/value-The existing industry standards do not consider the influence of buried depth and span in the evaluation of tunnel stability.The stability evaluation method of large section tunnel considering the correction of overburden span ratio proposed in this paper achieves higher accuracy for the stability evaluation of surrounding rock in a full or large-section mechanized excavation of double line high-speed railway tunnels.

Simple analytical model for depth-averaged velocity in meandering compound channels

A simple but applicable analytical model is presented to predict the lat- eral distribution of the depth-averaged velocity in meandering compound channels. The governing equation with curvilinear coordinates is derived from the momentum equation and the flow continuity equation under the condition of quasi-uniform flow. A series of experiments are conducted in a large-scale meandering compound channel. Based on the experimental data, a magnitude analysis is carried out for the governing equation, and two lower-order shear stress terms are ignored. Four groups of experimental data from different sources are used to verify the predictive capability of this model, and good predictions are obtained. Finally, the determination of the velocity parameter and the limitation of this model are discussed.

Numerical research on flow and thermal transport in cooling pool of electrical power station using three depth-averaged turbulence models

This paper describes a numerical simulation of thermal discharge in the cooling pool of an electrical power station, aiming to develop general-purpose computational programs for grid generation and flow/pollutant transport in the complex domains of natural and artificial waterways. Three depth-averaged two-equation closure turbulence models, k-ε, k- w, and k- w, were used to close the quasi three-dimensional hydrodynamic model. The k- w model was recently established by the authors and is still in the testing process. The general-purpose computational programs and turbulence models will be involved in a software that is under development. The SIMPLE （Semi-Implicit Method for Pressure-Linked Equation） algorithm and multi-grid iterative method are used to solve the hydrodynamic fundamental governing equations, which are discretized on non-orthogonal boundary-fitted grids with a variable collocated arrangement. The results calculated with the three turbulence models were compared with one another. In addition to the steady flow and thermal transport simulation, the unsteady process of waste heat inpouring and development in the cooling pool was also investigated.

THE EQUATIONS OF COMPLETE DEPTH-AVERAGED TURBULENCE MODEL IN GENERAL ORTHOGONAL COORDINATES

For shallow water flow, the depth-averaged governing equations are derived by depth-averaging of the mean equations for three-dimensional turbulent flows. The influences of free water surface and of topography of river bed are taken into account.The depth-averaged equations of k-εturbulence model are also obtained. Because it Accounts for the three-dimensional effect, this model is named as the complete Depth-averaged model.The boundaries of natural water bodies are usually curved.In this work, the derived equations in Cartesian coordinates are transformed into orthogonal coordinates. The obtained equations can be applied directly to numerical computation of practical problems.

Comparison of depth-averaged concentration and bed load flux sediment transport models of dam-break flow

This paper presents numerical simulations of dam-break flow over a movable bed. Two different mathematical models were compared: a fully coupled formulation of shallow water equations with erosion and deposition terms(a depth-averaged concentration flux model), and shallow water equations with a fully coupled Exner equation(a bed load flux model). Both models were discretized using the cell-centered finite volume method, and a second-order Godunov-type scheme was used to solve the equations. The numerical flux was calculated using a Harten, Lax, and van Leer approximate Riemann solver with the contact wave restored(HLLC). A novel slope source term treatment that considers the density change was introduced to the depth-averaged concentration flux model to obtain higher-order accuracy. A source term that accounts for the sediment flux was added to the bed load flux model to reflect the influence of sediment movement on the momentum of the water. In a onedimensional test case, a sensitivity study on different model parameters was carried out. For the depth-averaged concentration flux model,Manning's coefficient and sediment porosity values showed an almost linear relationship with the bottom change, and for the bed load flux model, the sediment porosity was identified as the most sensitive parameter. The capabilities and limitations of both model concepts are demonstrated in a benchmark experimental test case dealing with dam-break flow over variable bed topography.

Flow and transport simulation of Madeira River using three depth-averaged two-equation turbulence closure models

This paper describes a numerical simulation in the Amazon water system, aiming to develop a quasi-three-dimensional numerical tool for refined modeling of turbulent flow and passive transport of mass in natural waters. Three depth-averaged two-equation turbulence closure models, k-ε,k-w, and k-w, were used to close the non-simplified quasi-three-dimensional hydrodynamic fundamental governing equations. The discretized equations were solved with the advanced multi-grid iterative method using non-orthogonal body-fitted coarse and fine grids with collocated variable arrangement. Except for steady flow computation, the processes of contaminant inpouring and plume development at the beginning of discharge, caused by a side-discharge of a tributary, have also been numerically investigated. The three depth-averaged two-equation closure models are all suitable for modeling strong mixing turbulence. The newly established turbulence models such as the k-w model, with a higher order of magnitude of the turbulence parameter, provide a possibility for improving computational precision.

深度小于30 m正常停钻V_(S30)预测公式精度分析

我国钻孔测速中在正常停孔条件下产生大量深度小于30 m的钻孔数据。由于正常停钻,我国几乎没有此类场地下深度超30 m的钻孔实测数据,故无法以同类场地大于30 m数据直接回归V_(S30)公式。国外区域数据建立的V_(S30)预测公式有区域性,其在场地特征类似才适用;针对我国深度小于30 m正常停孔下V_(S30)预测线性外插公式LEE为具有潜在可行性公式。因此,为了从已有公式中得到可靠的V_(S30)预测公式,基于地质宏观类比,在停钻深度没有到30 m数据条件下发展了对已有公式的精度分析方法。通过对平均剪切波速竖向分布特点的分析,提出“精度分析区间”;并在缺乏停钻深度到30 m直接验证数据的前提下,提出两种分析公式预测精度的方法:方法一中校核对象是实测数据,具有一定直接检验的特点,但仅适用于具有反算能力的公式;方法二是基于所有公式都具有的——换算深度越靠近30 m则V_(S30)预测越准确的特点提出的,适用范围广。以滇中引水工程为案例,应用两种方法于该工程中深度小于30 m的正常停钻数据,为该工程选出精度最高公式LEE。

漂浮植被作用下水流纵向流速的垂向分布及离散特性研究

为探究漂浮植被影响下明渠水流流速及纵向离散系数的沿程变化特性,采用Fluent软件中的k-ε模型进行三维数值模拟并与水槽试验结果进行对比分析,在模型验证合理的基础上,对漂浮植被不同根系下探深度及覆盖率下水流纵向时均流速的垂向分布特性进行研究,并基于改进的分区模型分析了含漂浮植被明渠的纵向离散系数。结果表明:漂浮植被水流垂向上可分为含植被水流层、无植被水流层与近河床层。纵向流速最大值出现在无植被水流层,其大小与植被下探深度及覆盖率呈正相关。含植被水流层的纵向流速随植被根系下探深度和覆盖率的增加而减小,无植被水流层及近河床层的纵向流速随着下探深度和覆盖率的增大而增大,且植被覆盖率及下探深度越大含植被水流层与无植被水流层的流速差异越大。纵向离散系数沿程表现出先增大后减小的趋势,在植被区中下游离散最为剧烈,且与植被下探深度和覆盖率呈正相关。

激光焊OCT熔深测量去噪及数据拟合方法研究

为了解决激光焊接熔深在线检测及光学相干光层析成像(OCT)熔深检测信号噪声多的问题,采用了一种百分位滤波加移动平均算法的熔深曲线拟合方法。通过光学相干光层析成像系统对304不锈钢匙孔焊过程进行了熔深在线检测,在使用百分位滤波从原始散点数据中提取出百分位熔深曲线过程中,发现该方法提取的百分位熔深曲线存在尖峰干扰噪声,通过移动平均算法对百分位熔深曲线进行低通滤波处理,最终从原始散点数据中提取拟合出OCT熔深测量曲线。结果表明,将OCT熔深测量曲线与焊缝纵抛面的实际熔深曲线进行对比,该方法获取OCT熔深测量曲线的测量精度最大提升了15%。该方法能从OCT原始散点数据中有效提取拟合出更为准确的OCT熔深测量曲线。

东北长白山泥炭地硅藻−水位埋深转换函数

本研究基于2016、2019和2021年夏季在东北长白山地区7处泥炭地采集的160个表层样品和环境因子数据,结合表层样品硅藻分析,构建了硅藻属种与环境因子数据库,该数据库包括64个硅藻属种和11个环境变量。优势硅藻属种组合沿水位埋深梯度(0~66 cm)呈现明显分异,偏典范对应分析结果表明,水位埋深单独解释了硅藻组合数据总方差的8.4%,远大于其他环境因子的单独解释份额。基于此,选取加权平均模型和最大似然估计模型构建硅藻−水位转换函数。不同模型分析结果显示,典型回归耐受值降权加权平均模型构建的硅藻−水位转换函数表现最佳,剔除残差大于20%水位梯度(13.2 cm)的样品后进行留一法交叉检验,该模型的推导值与实测值相关系数最大和推导误差最小。本文构建的硅藻−水位转换函数为定量反演长白山地区泥炭地过去水位变化提供了新的有效方法。

基于积雪数据的HBV模型改进及应用

大渡河流域内站点分布较少,历史观测数据不足,给该地区的融雪径流预报带来困难。基于欧洲中期天气预报中心提供的最新一代高分辨率陆面再分析数据集ERA5-Land,将积雪覆盖率和积雪平均深度引入度日因子雪量计算公式中,对HBV模型的积融雪模块进行改进,以提升融雪径流计算的可靠性。以大渡河上游为研究对象,选取1961—2018年的水文气象资料对模型进行率定和验证,并以2019年为例进行试预报研究。结果表明,通过引入ERA5-Land再分析数据,以及对积融雪模块进行改进,发挥了其在模拟积融雪上的优势,有效提升了融雪径流预报精度,对大渡河流域具有适用性。研究成果可为稀缺资料地区融雪径流模拟预报提供经验。

基于转置注意力的多尺度深度融合单目深度估计

单目深度估计是计算机视觉领域中一项基础任务,其目标是通过单张图像预测深度图,并获取每个像素位置的深度信息。本文提出一种新的单目深度估计网络结构,旨在进一步提高网络的预测准确性。转置注意力机制在降低参数量和计算量的同时引入了自注意力机制,以关注图像中的特定区域,并结合不同通道之间的信息。这种机制能够有效地关注到图像中的细小区域和边缘信息,并进行学习。本文还提出一种改进的转置注意力机制,以更少的参数量保留语义信息。多尺度深度融合根据不同通道提取不同深度特征的特点,计算每个通道的平均深度,以增强模型的深度感知能力。此外,它能够建模垂直距离的长距离关系,有效地分离物体之间的边缘,有助于减少细粒度信息的损失。最后,本文在NYU Depth V2数据集和KITTI数据集上进行实验,验证了所提出模块的有效性,并取得了出色的性能表现。

考虑综合成本的常规公交客流分配方法

为改善常规公交客流数据传统调查方法效率低、准确性差,以及常规公交客流分配时对出行成本考虑不全面、个体间出行成本存在较大差距的缺点,开展了考虑综合成本的常规公交客流分配方法研究。以数据即服务为基础开发的手机信令数据平台作为常规公交客流分配数据来源。通过经纬度坐标匹配,得到用户与交通小区之间的空间关系。利用数据仓库工具筛取数据字典索引,界定时间、速度、起终点类型等数据参数,通过时间匹配、路径匹配进行交通方式识别,将用户比例外推扩样至全国人口,得到常驻居民早高峰常规公交通勤起讫点(origin-destination,OD)量。分析常规公交客流个体的出行时间成本、拥挤成本、票价成本,建立以个体利益最大为原则、考虑综合成本的常规公交客流分配模型。将交通小区间常规公交客流分配问题转换为有向赋权图路径选择问题,并采用深度优先搜索与连续平均法混合算法求解,进行常规公交出行方案筛选以及客流分配。选取哈尔滨市典型交通小区为案例,开展常规公交客流分配,并与传统Logit路径选择概率模型分配结果、人工调查结果对比分析。结果表明:模型分配结果与人工调查结果的平均绝对百分比误差为4%,Logit模型为17.5%。模型分配客流后个体出行成本极差、方差、总和分别为0.03,0.0001,1108.35,Logit模型分别为3.28,1.58,1127.02。验证了模型分配客流的准确性以及考虑综合成本的必要性,分配客流后个体出行成本差距更小,更符合利益最大原则。

Modeling and Validation of Indentation Depth of Abrasive Grain into Lithium Niobate Wafer by Fixed-Abrasive Lapping

The prediction of indentation depth of abrasive grain in hydrophilic fixed-abrasive(FA)lapping is crucial for controlling material removal rate and surface quality of the work-piece being machined.By applying the theory of contact mechanics,a theoretical model of the indentation depth of abrasive grain was developed and the relationships between indentation depth and properties of contact pairs and abrasive back-off were studied.Also,the average surface roughness(Ra)of lapped wafer was approximately calculated according to the obtained indentation depth.To verify the rationality of the proposed model,a series of lapping experiments on lithium niobate(LN)wafers were carried out,whose average surface roughness Ra was measured by atomic force microscope(AFM).The experimental results were coincided with the theoretical predictions,verifying the rationality of the proposed model.It is concluded that the indentation depth of the fixed abrasive was primarily affected by the applied load,wafer micro hardness and pad Young′s modulus and so on.Moreover,the larger the applied load,the more significant the back-off of the abrasive grain.The model established in this paper is helpful to the design of FA pad and its machining parameters,and the prediction of Ra as well.

Crack elongation and its width of large depth reinforced concrete beams

In order to meet the requirement of structural inspection,the crack spacing and crack width at various heights in the tensile zone of six large depth reinforced concrete beams were measured under several loading levels of serviceability state.The effects of the depth of normal section beams on the crack spacing and crack width were analyzed,and the modified model is proposed for calculating the average crack spacing by thinking about the depth of normal section,the reinforcement arrangement and the effective reinforcement ratio.The relationships of crack widths at any position in the tensile zone and at the reinforcement level on the side surface of beam were studied.By theoretical and statistical analysis,a method is proposed to calculate the ratios of crack widths between any position and the reinforcement level on the side surface of large depth reinforced concrete beams.

Signal averaging for noise reduction in anesthesia monitoring and control with communication channels

This paper investigates impact of noise and signal averaging on patient control in anesthesia applications, especially in networked control system settings such as wireless connected systems, sensor networks, local area networks, or tele-medicine over a wide area network. Such systems involve communication channels which introduce noises due to quantization, channel noises, and have limited communication bandwidth resources. Usually signal averaging can be used effectively in reducing noise effects when remote monitoring and diagnosis are involved. However, when feedback is intended, we show that signal averaging will lose its utility substantially. To explain this phenomenon, we analyze stability margins under signal averaging and derive some optimal strategies for selecting window sizes. A typical case of anesthe-sia depth control problems is used in this development.

基于特征融合与通道感知的无人机红外目标跟踪算法

针对手工提取特征对红外目标不敏感,导致无法准确跟踪红外目标的问题,在全卷积孪生网络框架下,融合多层深度特征并结合通道感知提出了一种无人机红外目标跟踪算法。首先使用预训练网络提取目标深度特征,分别提取待跟踪目标的Conv4-1、Conv4-3、Conv5-2层特征,进而通过梯度计算选择对于目标活动和尺度变化较为敏感的特征通道参与后序的互相关操作,并通过计算模板图像和候选区域搜索图像之间的相似度获取目标响应图。最后利用平均峰值相关能量对跟踪结果进行评估并使用卡尔曼滤波对跟踪结果进行修正。在LSOTB-TIR红外目标跟踪数据集上进行了性能测试并与当前九种优秀的算法进行了对比,实验结果表明,本文算法跟踪成功率最高,能够有效应对红外目标跟踪中热交叉、干扰源等挑战,且具有较好的实时性。

基于VMD-MA的GNSS-MR雪深反演方法

针对利用全球卫星导航系统多径反射(GNSS-MR)技术反演雪深过程中信噪比(SNR)序列趋势项分离不佳和反演结果波动较大的问题,提出一种基于变分模态分解(VMD)和移动平均(MA)的雪深反演方法。VMD算法通过自适应高通滤波有效分离SNR序列的趋势项,MA算法对初始反演结果进行平滑处理从而减少随机波动。选用瑞典KIRU站2021年前5个月GLONASS不同频段的SNR观测值开展实验,研究所提方法的可行性。结果表明:基于VMD算法的反演结果与气象站原位雪深相关系数超过0.95,均方根误差(RMSE)最低约5 cm,较传统算法减少近40%;经MA算法平滑处理后,反演精度进一步提高。考虑到GNSS站和气象站之间的差异性,选取GPS SNR反演结果作为参考数据源,不同参考数据源取得了一致的实验结论,验证了所提方法的可行性和有效性。

基于深平均流预测模型的水下滑翔机路径优化

随着水下滑翔机在海洋调查及声学探测领域的广泛运用,精准、高效控制其路径对精细化海洋观测至关重要。针对水下滑翔机受海流影响产生较大偏航差问题,采用最小二乘支持向量机法(LSSVM)预测深平均流,以单剖面偏航差最小为目标函数,以实际航向与计划航向夹角不超过一定值为约束条件,构建非线性约束极值模型,确定预设剖面最优目标航向及出水点坐标,从而实现路径优化目的。采用“海燕-II”型水下滑翔机历史数据进行验证,结果表明:1) LSSVM法预测深平均流准确性较高,但当局部流向有明显变化时预测效果不佳,取前3个剖面数据作为训练样本时预测效果更好;2)采用文中方法优化后,水下滑翔机路径更稳定,各剖面偏航差平均为281.1 m。

基于改进CNN的苹果缺陷检测方法研究

目的:解决现有苹果缺陷检测方法存在的精度低、效率差等问题。方法:基于水果图像采集系统,提出一种改进的卷积神经网络用于苹果表面缺陷检测;引入深度可分离卷积代换原网络标准卷积,提高特征提取速度;引入Leaky ReLU激活函数代替ReLU激活函数,提高计算效率和精度;引入全局平均池化替换全连接层,降低网络模型的计算量;并在每层卷积后加入批量归一化层,通过试验与常规方法进行对比分析,验证其优越性。结果:与常规方法相比,所提方法在苹果缺陷检测中具有较高的检测准确率和速度,且模型参数量少,准确率达99.60%,检测速度(每秒帧数)达526,模型参数量为389 072。结论:该苹果缺陷检测方法能有效降低模型参数和检测时间,具有较高的准确率和速度。