Influence of confined water on the limit support pressure of tunnel face in weakly water-rich strata

In the process of shield tunneling through soft soil layers,the presence of confined water ahead poses a significant threat to the stability of the tunnel face.Therefore,it is crucial to consider the impact of confined water on the limit support pressure of the tunnel face.This study employed the finite element method(FEM)to analyze the limit support pressure of shield tunnel face instability within a pressurized water-containing layer.Subsequently,a multiple linear regression approach was applied to derive a concise solution formula for the limit support pressure,incorporating various influencing factors.The analysis yields the following conclusions:1)The influence of confined water on the instability mode of the tunnel face in soft soil layers makes the displacement response of the strata not significant when the face is unstable;2)The limit support pressure increases approximately linearly with the pressure head,shield tunnel diameter,and tunnel burial depth.And inversely proportional to the thickness of the impermeable layer,soil cohesion and internal friction angle;3)Through an engineering case study analysis,the results align well with those obtained from traditional theoretical methods,thereby validating the rationality of the equations proposed in this paper.Furthermore,the proposed equations overcome the limitation of traditional theoretical approaches considering the influence of changes in impermeable layer thickness.It can accurately depict the dynamic variation in the required limit support pressure to maintain the stability of the tunnel face during shield tunneling,thus better reflecting engineering reality.

前列腺癌患者血清TWEAK和SREBP-1水平表达与临床病理特征及无进展生存预后的关系研究

目的 研究前列腺癌(prostate cancer,PC)患者血清肿瘤坏死因子样弱凋亡诱导因子(tumor necrosis factor like weak inducer of apoptosis,TWEAK)、固醇调节元件结合蛋白1(sterol regulatory element-binding protein 1,SREBP-1)表达与临床病理特征及无进展生存预后的关系。方法 选取2018年1月~2020年1月武汉市东西湖区人民医院行PC根治术的94例PC患者为PC组,以同期50例前列腺增生(benign prostatic hyperplasia,BPH)患者为BPH组,以同期体检的50例健康人为对照组。酶联免疫吸附试验(enzyme-linked immunosorbent assay,ELISA)检测血清TWEAK和SREBP-1表达水平。Kaplan-Meier生存分析比较血清TWEAK和SREBP-1对PC患者无进展生存预后的影响。多因素COX回归分析影响PC患者无进展生存预后的因素。结果PC组患者血清TWEAK(77.14±15.46 ng/L),SREBP-1(334.14±33.81 ng/L)高于BPH组(38.69±10.58 ng/L,201.69±28.74 ng/L)和对照组(36.26±10.27 ng/L,189.51±27.65 ng/L),差异具有统计学意义(t=23.752,25.249;34.636,37.821,均P<0.05)。PC患者血清TWEAK与SREBP-1表达呈显著正相关(r=0.668,P=0.001)。Gleason评分> 7分、TNM分期Ⅲ期及术前前列腺特异抗原(prostate specific antigen,PSA)水平≥20 ng/ml的PC患者血清TWEAK,SREBP-1水平高于Gleason评分≤7分,TNM分期Ⅰ~Ⅱ期及术前PSA水平<20 ng/ml,差异具有统计学意义(t=8.465~16.597,均P<0.05)。TWEAK高表达组和低表达组三年总体无进展生存率分别为60.42%(29/48)和86.96%(40/46),SREBP-1高表达组和低表达组三年总体无进展生存率分别为57.78%(26/45)和87.76%(43/49);TWEAK高表达组、SREBP-1高表达组三年累积无进展生存率低于TWEAK低表达组、SREBP-1低表达组,差异具有统计学意义(Log-rankχ2=8.125,9.547,P=0.004,0.002)。TNM分期Ⅲ期(OR=1.448,P <0.001)、Gleason评分> 7分(OR=1.401,P <0.001)、术前PSA≥20 ng/ml (OR=1.353,P <0.001)及血清TWEAK (OR=1.338,P <0.001)和SREBP-1 (OR=1.293,P <0.001)是影响PC患者无进展生存预后的独立危险因素。结论 PC患者血清TWEAK和SREBP-1升高,两者与PC临床病理特征相关,是评估无进展生存预后的血清标志物。

Weak Galerkin Finite Element Method for the Unsteady Stokes Equation

The Weak Galerkin (WG) finite element method for the unsteady Stokes equations in the primary velocity-pressure formulation is introduced in this paper. Optimal-order error estimates are established for the corresponding numerical approximation in an H1 norm for the velocity, and L2 norm for both the velocity and the pressure by use of the Stokes projection.

Weakly Singular Symmetric Galerkin Boundary Element Method for Fracture Analysis of Three-Dimensional Structures Considering Rotational Inertia and Gravitational Forces

The Symmetric Galerkin Boundary Element Method is advantageous for the linear elastic fracture and crackgrowth analysis of solid structures,because only boundary and crack-surface elements are needed.However,for engineering structures subjected to body forces such as rotational inertia and gravitational loads,additional domain integral terms in the Galerkin boundary integral equation will necessitate meshing of the interior of the domain.In this study,weakly-singular SGBEM for fracture analysis of three-dimensional structures considering rotational inertia and gravitational forces are developed.By using divergence theorem or alternatively the radial integration method,the domain integral terms caused by body forces are transformed into boundary integrals.And due to the weak singularity of the formulated boundary integral equations,a simple Gauss-Legendre quadrature with a few integral points is sufficient for numerically evaluating the SGBEM equations.Some numerical examples are presented to verify this approach and results are compared with benchmark solutions.

Fractional Envelope Analysis for Rolling Element Bearing Weak Fault Feature Extraction

The bearing weak fault feature extraction is crucial to mechanical fault diagnosis and machine condition monitoring. Envelope analysis based on Hilbert transform has been widely used in bearing fault feature extraction. A generalization of the Hilbert transform, the fractional Hilbert transform is defined in the frequency domain, it is based upon the modification of spatial filter with a fractional parameter, and it can be used to construct a new kind of fractional analytic signal. By performing spectrum analysis on the fractional envelope signal, the fractional envelope spectrum can be obtained. When weak faults occur in a bearing, some of the characteristic frequencies will clearly appear in the fractional envelope spectrum. These characteristic frequencies can be used for bearing weak fault feature extraction. The effectiveness of the proposed method is verified through simulation signal and experiment data. © 2017 Chinese Association of Automation.

Flexural and eigen-buckling analysis of steel-concrete partially composite plates using weak form quadrature element method

Flexural and eigen-buckling analyses for rectangular steel-concrete partially composite plates(PCPs)with interlayer slip under simply supported and clamped boundary conditions are conducted using the weak form quadrature element method(QEM).Both of the derivatives and integrals in the variational description of a problem to be solved are directly evaluated by the aid of identical numerical interpolation points in the weak form QEM.The effectiveness of the presented numerical model is validated by comparing numerical results of the weak form QEM with those from FEM or analytic solution.It can be observed that only one quadrature element is fully competent for flexural and eigen-buckling analysis of a rectangular partially composite plate with shear connection stiffness commonly used.The numerical integration order of quadrature element can be adjusted neatly to meet the convergence requirement.The quadrature element model presented here is an effective and promising tool for further analysis of steel-concrete PCPs under more general circumstances.Parametric studies on the shear connection stiffness and length-width ratio of the plate are also presented.It is shown that the flexural deflections and the critical buckling loads of PCPs are significantly affected by the shear connection stiffness when its value is within a certain range.

Analysis of the effects of weak floor strata onlongwall face stability using finite element modeling

Higher production, better safety standard, and potential for automation are some of the benefits of longwall mining. Today, longwall face advances at a faster rate exposing many diversified rock layers in a short period of time. It is now a serious challenge to cope with ground control problems such as roof falls, face and floor failure, and excessive shield loading as fast as possible to minimize production and monetary losses. In Illinois Coal Mines, the existence of weak floor strata blow the coal seam may pose additional problems related to floor heaving, shield base punching, and associated roof and face falls. In this study, the effects of weak floor on longwall ground control are analyzed using two dimensional finite element models. A two leg 635 6 ton (700 short ton) yielding capacity shield is included in the models to evaluate the effects of different thickness and material properties of the weak floor. The study indicates that the thickness and material properties of weak floor have significant effects on shield loading, the distribution and intensity of front abutment stress, failure zones in the surrounding strata, roof to floor convergence, and floor punching by the shield base.

A Modified Weak Galerkin Finite Element Method for the Biharmonic Equation on Polytopal Meshes

A modified weak Galerkin(MWG)finite element method is developed for solving the biharmonic equation.This method uses the same finite element space as that of the discontinuous Galerkin method,the space of discontinuous polynomials on polytopal meshes.But its formulation is simple,symmetric,positive definite,and parameter independent,without any of six inter-element face-integral terms in the formulation of the discontinuous Galerkin method.Optimal order error estimates in a discrete H2 norm are established for the corresponding finite element solutions.Error estimates in the L^(2)norm are also derived with a sub-optimal order of convergence for the lowest-order element and an optimal order of convergence for all high-order of elements.The numerical results are presented to confirm the theory of convergence.

A Weak Galerkin Harmonic Finite Element Method for Laplace Equation

In this article,a weak Galerkin finite element method for the Laplace equation using the harmonic polynomial space is proposed and analyzed.The idea of using the P_(k)-harmonic polynomial space instead of the full polynomial space P_(k)is to use a much smaller number of basis functions to achieve the same accuracy when k≥2.The optimal rate of convergence is derived in both H^(1)and L^(2)norms.Numerical experiments have been conducted to verify the theoretical error estimates.In addition,numerical comparisons of using the P_(2)-harmonic polynomial space and using the standard P_(2)polynomial space are presented.

Planar Weak Form Quadrature Beam Elements Based on Absolute Nodal Coordinate Formulation: A Structural Mechanics Approach

A planar nonlinear weak form quadrature beam element of arbitrary number of axial nodes is proposed on the basis of the absolute nodal coordinate formulation (ANCF). Elastic forces of the element are established through geometrically exact beam theory, resulting in good consistency with classical beam theory. Two examples with strong geometrical nonlinearity are presented to verify the effec-tiveness of the formulation.

Four-Order Superconvergent Weak Galerkin Methods for the Biharmonic Equation on Triangular Meshes

A stabilizer-free weak Galerkin(SFWG)finite element method was introduced and analyzed in Ye and Zhang(SIAM J.Numer.Anal.58:2572–2588,2020)for the biharmonic equation,which has an ultra simple finite element formulation.This work is a continuation of our investigation of the SFWG method for the biharmonic equation.The new SFWG method is highly accurate with a convergence rate of four orders higher than the optimal order of convergence in both the energy norm and the L^(2)norm on triangular grids.This new method also keeps the formulation that is symmetric,positive definite,and stabilizer-free.Four-order superconvergence error estimates are proved for the corresponding SFWG finite element solutions in a discrete H^(2)norm.Superconvergence of four orders in the L^(2)norm is also derived for k≥3,where k is the degree of the approximation polynomial.The postprocessing is proved to lift a P_(k)SFWG solution to a P_(k+4)solution elementwise which converges at the optimal order.Numerical examples are tested to verify the theor ies.

广义弱形式自由单元法

自由单元法(FrEM)是一种单元配点法,吸收了有限元法等参单元的插值稳定性与无网格法使用灵活的优点,具有稳定性好和灵活性高的性能.FrEM在每个配置点只需要一个通过自由选择周围节点而形成的独立的等参单元,不需要考虑单元之间节点的相互连接关系,这种自由性使得人们可以按照学科性质形成所需要的单元,因而FrEM既适用于固体力学,也适用于流体力学问题的求解.然而,FrEM所用单元需要至少有一个内部节点(用于方程的配点),以致有限元法中单元节点相连的网格不能在FrEM中直接使用.文章基于对应于配置点的等参单元形函数在与其不相连的边界上为0的特性和配置点等效节点力平衡关系,提出了一种广义弱形式自由单元法(GFrEM).该方法是一种使用单元逐点建立配置方程的单元配点法,具有如下特点:(1)突破了现有自由单元法中单元需要内部节点的限制,因而可以使用线性单元和高阶单元;(2)突破了现有自由单元法中一个配置点使用一个单元的限制,可以使用与配置点相连的任意多个单元;(3)可以使用任意形式的规则单元和多边形/多面体单元;(4)如果使用单元节点相连的传统有限元法网格,则GFrEM自然演变为传统的有限元法.论文将给出几个固体力学方面的应用算例,展示所提方法的有效性.

长期运行引水隧洞开裂衬砌受力影响规律与承载特性

衬砌裂缝是引水隧洞中常见的病害之一,衬砌开裂会对隧洞衬砌承载力和安全性造成不同程度的影响。以长期服役的东江水源工程引水隧洞衬砌为研究对象,通过现场检测确定了全洞段裂缝的产状、分布规律和开裂特征。利用ANSYS软件中的软弱薄层单元,建立了开裂衬砌的三维数值模型,得出贯穿型纵向裂缝的位置变化对衬砌结构安全性的影响,系统分析了衬砌的承载特性。结果表明,衬砌开裂条件下,衬砌结构局部开裂区的安全系数降低最为显著,尤其是拱肩位置的裂缝对结构的危害程度远大于边墙、拱顶裂缝;另外,裂缝的产生会对其他未开裂部位的受力特性及稳定性产生影响。数值模拟结果良好地体现了裂损衬砌对隧洞结构的影响规律,与现场检测结果一致,为长期服役下隧洞结构病害防治提供了参考。

深地万米井测井电缆强度分析

中国超深层油气资源潜力巨大,推进超深层油气勘探、实现新层系突破是开拓油气新领域的重点方向。针对深地某科探井万米电缆遇卡等问题,采用截面法,建立电缆在井下、天滑轮、地滑轮、滚筒等位置处的有限元模型,研究拉力棒、滚筒直径、上提速度对万米测井电缆强度的影响。计算结果表明:为保证在电缆不断的情况下使设置的弱点先断,并为电缆保留一定安全系数,可以选用5000lbf^(*)拉力棒;选用大直径的滚筒来减小电缆张力,优先选用直径700mm的滚筒;测井电缆正常上提工作速度取6000m/h,此时电缆张力可达61.4kN,满足强度要求。研究成果为深地万米井测井作业电缆、滚筒、拉力棒的选取提供了基础数据。

H型钢弱轴撞击后剩余力学性能与损伤评估

工业厂房中的H型钢常遭受吊物与车辆撞击,且撞击方向具有不确定性.基于此,本文针对H型钢弱轴撞击后剩余力学性能与损伤评估进行研究.首先,通过试验获得了弱轴撞击后破坏形态、荷载位移曲线与应变发展特征.其次,基于有限元模型重点分析了撞击质量、撞击速度与轴压比对剩余承载力的影响,并提出了H型钢弱轴撞击后剩余承载力预测公式.研究结果表明:试件受压以整体弯曲变形为主,翼缘与腹板均未发生明显局部变形;撞击后试件刚度与承载力明显降低,但仍保持较好的延性;撞击能量与轴压比是影响剩余承载力的关键因素;基于撞击质量、撞击速度与受撞时轴压比建立了m-v-n损伤评估曲面图,可根据撞击工况评估H型钢弱轴受撞损伤程度.

带PEC柱钢板剪力墙结构(弱轴连接)抗震性能有限元分析

为研究边缘柱为部分外包混凝土组合柱的钢板剪力墙结构(弱轴连接)的抗震性能,使用有限元软件ABAQUS完成1榀边缘柱为H型钢柱、5榀边缘柱为PEC柱的钢板剪力墙结构(弱轴连接)在循环荷载作用下的有限元数值模拟,得到结构的应力分布、破坏模式、滞回曲线、耗能性能、骨架曲线以及刚度退化曲线,并完成了1榀带PEC柱的钢板剪力墙结构(弱轴连接)的试验,验证了有限元模拟的正确性.分析表明在钢板剪力墙结构中(弱轴连接),将PEC柱作为剪力墙的边缘框架柱,同样可以很好的约束屈曲后的钢板剪力墙,使其充分发挥屈曲后的性能,显著提升整体结构的抗侧刚度、承载力以及耗能性能.

邻近寺庙群高海拔隧道钻爆施工关键技术研究

为解决同赛高速隧道施工中振动风险高、作业面不足、洞身超挖的问题,自主研究开发爆破风险识别程序,基于地质背景与施工条件,采用现场试验、数值模拟、工程实测等方式,开展隧道钻爆布孔形式、装药结构、轮廓线等技术参数优化研究。现场实践表明:通过应用研发振动风险识别程序,可大幅度提高现场振动风险识别、动态控制能力,有效避免了敏感人群、建筑群受扰动风险;依据现场有效作业面设大倾角掏槽布孔,辅以扩槽孔、拱顶单排下压孔等措施,在满足掏槽、破岩要求的前提下达到了提升工效的预期;采用优化周边孔装药结构、收紧拱顶轮廓线等措施,有效降低了洞身排险后超挖量,现场初支喷混超方量由200%降低至100%以内,同时每循环节省药量约20kg,经济效益显著。

含软弱夹层隧道围岩渗流稳定性离散元分析

软弱夹层和地下水渗流作用均对隧道开挖时的围岩稳定性有重要影响.依托蒙华铁路中条山隧道工程,搭建了PFC-FLAC流固耦合模拟平台,通过与均质围岩隧道位移理论解作对比,验证了该平台模拟渗流作用下隧道开挖时围岩力学响应的可靠性.在此基础上,对地下水渗流作用下含软弱夹层隧道围岩的失稳破坏过程进行了非连续数值模拟,深入分析了隧道开挖后围岩位移场、应力场、裂纹动态发展规律及能量场演化规律,研究了复杂水文地质条件下隧道围岩失稳破坏机理.结果表明:隧道开挖后的围岩破坏形式表现为顶部软弱夹层区域出现大量张拉和剪切裂纹,软弱夹层和少部分砾岩逐渐剥落破坏.洞周围岩迅速形成一个带有缺口的接触力链环,环内围岩应力卸载明显,洞周围岩的应变能密度差值均呈现先减小后回升的规律.

含软弱夹层的隧道洞口边坡稳定性分析

软弱夹层对边坡的稳定性影响突出,是坡体潜在的滑移面。为了研究含软弱夹层的隧道洞口边坡在开挖施工和隧道掘进过程中的稳定性,使用MIDAS GTS/NX软件对施工全过程进行模拟,通过强度折减法(SRM)计算洞口边坡的稳定系数。所得结果表明:洞口开挖施工会破坏原有地应力平衡,导致坡顶土体出现张拉裂缝。隧道掘进施工过程中,洞口边坡的稳定系数会随着掘进过程而降低,考虑到隧道爆破施工震动,加之软弱夹层的不利因素,建议在工程设计施工中将锚杆长度增加至10m,控制软弱夹层的蠕变滑移,防止边坡失稳。

一类非线性四阶p-拉普拉斯型方程的弱解存在性

利用极小元法对一类非线性四阶p-Laplace方程进行求解,其中极小元法的基本内容是确定微分方程对应泛函的极小元,并由此证明微分方程弱解存在性。首先根据已知的微分方程在分部积分意义下对应的函数构造泛函,且极小元处的方程满足弱解的定义,其次将弱解存在性问题转化为方程对应泛函极小元存在性问题,最后证明了方程弱解的唯一性,最终得出结论,存在唯一弱解满足此类非线性四阶p-Laplace方程。