矿井巷道地球物理方法超前探测研究进展与展望

矿井直流电阻率法具有施工效率高、成本低的特点,广泛应用于煤矿掘进工作面水害超前探测。随着应用的不断深入,对矿井直流电阻率法超前探测信号处理方法提出了更高的要求。基于有限元方法和数据重构所得响应信息库,采用Levenberg-Marquardt人工神经网络方法实现了矿井直流电阻率法超前预测。首先采用非结构网格剖分和BiCGSTAB迭代有限元法建立了直流电阻率法超前探测模型,基于EMD方法实现数值计算响应与实测响应匹配,并提出了基于异常体超前距离与其异常率的预测机制,得到3 000组23维重构响应;然后,采用L-M算法构建了人工神经网络模型;最后,基于训练好的网络对数值计算响应和实测数据进行预测分析。研究表明：针对数值模拟响应,基于L-M人工神经网络的矿井直流电阻率法超前预测方法可有效预测100 m范围内的水害异常,预测网络均方误差为0.002 47,测试样本显示最大距离误差小于0.6 m;针对实测数据发现,该神经网络在全区段预测准确率为67%,当预测异常位置在15~80 m时预测准确率超过85%,基于L-M算法的人工神经网络可应用于直流电阻率法超前预测。研究成果对煤矿井下掘进工作面直流电阻率法超前探测方法的完善与推广应用有重要意义。

     

两种孔径网具对大洋微(小)型浮游植物调查结果的影响——以西南印度洋海域第34次大洋春季航次为例

浮游植物拖网是海洋浮游植物调查的重要工具,不同网具可以导致不同的调查结果。为研究两种孔径网具对大洋浮游植物调查的影响,于2015年4~5月在西南印度洋分别用筛绢孔径为20和77 μm的两种浮游生物网在多个站位进行浮游植物采样。对采集的样品进行浮游植物鉴定,分析比较了两者浮游植物的物种数、细胞丰度、物种丰富度、多样性指数、均匀度指数和优势种。结果表明,在相同采样站位,筛绢孔径为20 μm网采样品鉴定得到的平均物种数、平均细胞丰度和平均物种丰富度分别是筛绢孔径为77 μm网采样品的2.7、17和2倍,呈显著差异。但两种网采样品的平均多样性指数和平均均匀度指数都无显著差异。此外,筛绢孔径为20 μm网采样品中有9种优势种,而筛绢孔径为77 μm网采样品中有11种优势种,其中共同的优势种有6种。以上结果说明在寡营养海域使用20 μm孔径的网具可以获得更为全面的浮游植物信息。     

Some numerical issues using element‐free Galerkin mesh‐less method for coupled hydro‐mechanical problems

A new formulation of the element‐free Galerkin (EFG) method is developed for solving coupled hydro‐mechanical problems. The numerical approach is based on solving the two governing partial differential equations of equilibrium and continuity of pore water simultaneously. Spatial variables in the weak form, i.e. displacement increment and pore water pressure increment, are discretized using the same EFG shape functions. An incremental constrained Galerkin weak form is used to create the discrete system equations and a fully implicit scheme is used for discretization in the time domain. Implementation of essential boundary conditions is based on a penalty method. Numerical stability of the developed formulation is examined in order to achieve appropriate accuracy of the EFG solution for coupled hydro‐mechanical problems. Examples are studied and compared with closed‐form or finite element method solutions to demonstrate the validity of the developed model and its capabilities. The results indicate that the EFG method is capable of handling coupled problems in saturated porous media and can predict well both the soil deformation and variation of pore water pressure over time. Some guidelines are proposed to guarantee the accuracy of the EFG solution for coupled hydro‐mechanical problems. Copyright © 2008 John Wiley & Sons, Ltd.     

复杂区域自适应三角形网格全自动生成方法

为了使用自适应有限单元法求解岩土工程问题，本文在行被法的基础上，提出了一种适用于多介质复杂区域的三角形网格全自动生成方法。文中给出三个工程算例．     

Load testing of anchors for wire mesh and cable net rockfall slope protection systems

This study presents results of field tests conducted on anchors used to support wire mesh and cable net rockfall protection systems. The load transfer and failure characteristics of these anchors are different from those used in most civil applications in that loads are often applied transversely to the top of tendon rather than axially. The study included vertical as well as horizontal series of tests conducted on some anchors widely used in wire mesh and cable net rockfall protect systems. It was found that the deformation characteristics of these anchors under vertical loading are nonlinear. They are approximated by a hyperbolic formulation and used to calculate the ultimate capacity. Top-downward progressive cracking of the grout was observed during loading and influences the deformation characteristics of these anchors under horizontal loading. The anchors deflected excessively before they could attain their ultimate capacity in the horizontal direction. Based on the field tests, it appears that the deformation under horizontal loading in the systems can be limited by using an enlarged grout zone at the top.     

Numerical investigation of the immersion ratio effects on ventilation phenomenon and also the performance of a surface piercing propeller

Surface Piercing Propellers (SPP) show high efficiency at high advance speeds. Regarding operational conditions, this kind of propellers generate an air layer when entering the water due to the rotation of the propeller; this phenomenon is called ventilation. The ventilation phenomenon divided into some mechanism with respect to air cavity length on the propeller surface; among them are partially ventilation mechanism and fully ventilation mechanism which has great importance. In this study, using numerical simulation, we have investigated ventilation patterns and also the performance of a five-blade SPP propeller (SPP 5.74) at immersion ratio of 33, 40, 50and 70% respectively. We used Sliding Mesh Technique for modeling. Also, we applied the volume of fluid method to simulate the open surface pattern. To validate numerical results, the four-blade propeller, 841-B was simulated, and then the results of thrust and torque coefficients compared with Olofsson experimental results and validated accordingly. The findings indicate that the maximum value for thrust and torque coefficient would occur at immersion ratio of 70% and the maximum propeller efficiency occurs at immersion ratio of 33% and advance coefficient of 1.1; Moreover, the critical advance coefficient (at the partially and the fully ventilation boundary) increases by a reduction in immersion ratio, so that critical advance coefficients are 0.6 and 0.76, respectively at immersion ratios of 70 and 33%. Meanwhile, as advance coefficient increases, length of ventilation zone will decrease, and consequently the propeller will be laid on partial ventilation zone.     

Occurrence and ingestion of microplastics by zooplankton in Kenya's marine environment: first documented evidence

Microplastics can be ingested by marine organisms and may lead to negative impacts at the base of marine food chains. This study investigated the occurrence and composition of microplastics in the sea-surface water and sought evidence of ingestion by zooplankton. Surface seawater was collected using a stainless-steel bucket and sieved directly through a stainless-steel sieve (250-µm mesh), while a 500-μm mesh net was towed horizontally to collect zooplankton, at 11 georeferenced stations off the Kenyan coast in February 2017, on board the national research vessel RV Mtafiti. Microplastic particles were sorted and characterised using an Optika dissecting microscope. Polymer types were identified using an ALPHA Platinum attenuated total reflection—Fourier-transform infrared (ATR-FTIR) spectrometer. A total of 149 microplastic particles, with an average abundance of 110 particles m^–3, were found in the surface seawater. A total of 129 particles were found ingested by zooplankton groups, where Chaetognatha, Copepoda, Amphipoda and fish larvae ingested 0.46, 0.33, 0.22 and 0.16 particles ind.^–1, respectively. Filaments dominated both the surface-water microplastics and the ingested microplastics, contributing 76% and 97% to those compositions, respectively. White particles were prevalent in the water (51%), whereas black was the colour found most commonly (42%) across the zooplankton groups. The sizes of particles that were in the water were in the range of 0.25–2.4 mm, and those ingested ranged between 0.01 and 1.6 mm. Polypropylene was predominant in the surface water, whereas low-density polyethylene was the most-ingested polymer type. The results provide the first documented evidence of the occurrence, composition and ingestion of microplastics by zooplankton in Kenya's marine environment, indicating that microplastics have the potential to enter pelagic food webs and cause pollution in the study area.     

Arbitrary Lagrangian–Eulerian method for large‐strain consolidation problems

In this paper, an arbitrary Lagrangian–Eulerian (ALE) method is generalized to solve consolidation problems involving large deformation. Special issues such as pore‐water pressure convection, permeability and void ratio updates due to rotation and convection, mesh refinement and equilibrium checks are discussed. A simple and effective mesh refinement scheme is presented for the ALE method. The ALE method as well as an updated‐Lagrangian method is then used to solve some classical consolidation problems involving large deformations with different constitutive laws. The results clearly show the advantage and efficiency of the ALE method for these examples. Copyright © 2007 John Wiley & Sons, Ltd.     

Simulating the hydraulic characteristics of the lower Yellow River by the finite‐volume technique

The finite‐volume technique is used to solve the two‐dimensional shallow‐water equations on unstructured mesh consisting of quadrilateral elements. In this paper the algorithm of the finite‐volume method is discussed in detail and particular attention is paid to accurately representing the complex irregular computational domain. The lower Yellow River reach from Huayuankou to Jiahetan is a typical meandering river. The generation of the computational mesh, which is used to simulate the flood, is affected by the distribution of water works in the river channel. The spatial information about the two Yellow River levee, the protecting dykes, and those roads that are obviously higher than the ground, need to be used to generate the computational mesh. As a result these dykes and roads locate the element interfaces of the computational mesh. In the model the finite‐volume method is used to solve the shallow‐wave equations, and the Osher scheme of the empirical function is used to calculate the flux through the interface between the neighbouring elements. The finite‐volume method has the advantage of using computational domain with complex geometry, and the Osher scheme is a method based on characteristic theory and is a monotone upwind numerical scheme with high resolution. The flood event with peak discharge of 15 300 m³/s, occurring in the period from 30 July to 10 August 1982, is simulated. The estimated result indicates that the simulation method is good for routing the flood in a region with complex geometry. Copyright © 2002 John Wiley & Sons, Ltd.     

Numerical simulation of viscous cavitating flow around a ship propeller

In the present study, cavitation and a ship propeller wake are reported by computed fluid dynamics based on viscous multiphase flow theory. Some recent validation results with a hybrid grid based on unsteady Navier-Stokes (N-S) and bubble dynamics equations are presented to predict velocity, pressure and vapor volume fraction in propeller wake in a uniform inflow. Numerical predictions of sheet cavitation, tip vortex cavitation and hub vortex cavitation are in agreement with the experimental data, same as numerical predictions of longitudinal and transversal evolution of the axial velocity. Blade and shaft rate frequency of propeller is well predicted by the computed results of pressure, and tip vortex is the most important to generate the pressure field within the near wake. The overall results indicate that the present approach is reliable for prediction of cavitation and propeller wake on the condition of uniform inflow.