A Hybrid Dung Beetle Optimization Algorithm with Simulated Annealing for the Numerical Modeling of Asymmetric Wave Equations

In the generalized continuum mechanics(GCM)theory framework,asymmetric wave equations encompass the characteristic scale parameters of the medium,accounting for microstructure interactions.This study integrates two theoretical branches of the GCM,the modified couple stress theory(M-CST)and the one-parameter second-strain-gradient theory,to form a novel asymmetric wave equation in a unified framework.Numerical modeling of the asymmetric wave equation in a unified framework accurately describes subsurface structures with vital implications for subsequent seismic wave inversion and imaging endeavors.However,employing finite-difference(FD)methods for numerical modeling may introduce numerical dispersion,adversely affecting the accuracy of numerical modeling.The design of an optimal FD operator is crucial for enhancing the accuracy of numerical modeling and emphasizing the scale effects.Therefore,this study devises a hybrid scheme called the dung beetle optimization(DBO)algorithm with a simulated annealing(SA)algorithm,denoted as the SA-based hybrid DBO(SDBO)algorithm.An FD operator optimization method under the SDBO algorithm was developed and applied to the numerical modeling of asymmetric wave equations in a unified framework.Integrating the DBO and SA algorithms mitigates the risk of convergence to a local extreme.The numerical dispersion outcomes underscore that the proposed SDBO algorithm yields FD operators with precision errors constrained to 0.5‱while encompassing a broader spectrum coverage.This result confirms the efficacy of the SDBO algorithm.Ultimately,the numerical modeling results demonstrate that the new FD method based on the SDBO algorithm effectively suppresses numerical dispersion and enhances the accuracy of elastic wave numerical modeling,thereby accentuating scale effects.This result is significant for extracting wavefield perturbations induced by complex microstructures in the medium and the analysis of scale effects.

考虑松动区高度影响的城市深埋隧道松动土压力研究

传统的太沙基松动土压力理论是基于浅埋地层这一基本假定建立的,其对于城市深埋地层不具备适用性。在深埋土质隧道土拱效应完全发挥情况下,考虑主应力轴旋转修正无黏性土侧压力系数计算方法;基于有限差分数值平台开展不同埋深、不同内摩擦角下的有限元模拟确定深埋黏性土层的破坏模式。给出考虑主应力轴旋转和内摩擦角对松动区高度影响的深埋无黏性土、黏性土地层的松动土压力计算公式,以实现对城市深埋土质隧道上覆土压力的准确计算。修正公式计算结果与文献、数值模拟结果对比分析结果表明:在深埋情况下,无黏性土层松动土压力修正公式计算结果与文献结果吻合良好;土体强度参数会对黏性土松动区高度造成影响,即随着内摩擦角的增大,松动区高度不断减小;黏性土层松动土压力修正公式计算结果与数值模拟结果吻合良好。

利用基于围陷波波形相关的网格搜索法确定昆仑山断裂带结构参数

提出了确定断层带结构的一种方法,它利用基于断层带围陷波波形相关的网格搜索法,以定量地确定断层带参数.该方法通过建立一系列由断层带的相关参数构建的断层带结构模型,利用有限差分方法数值模拟每组参数对应的断层带模型所产生的围陷波,并与实际观测围陷波波形进行相关分析,计算由以断层参数为多维网格坐标的相关系数变化趋势,网格搜索其峰值,最终获得最佳的一组参数,并确定断层带的结构.本文对昆仑山断裂带人工激发的围陷波进行分析,利用该方法确定了断裂带宽度和Q值参数.

水平井与非均质盒式油藏耦合模型

运用Green函数和Newman积原理,建立盒式油藏水平井产量计算模型.模型考虑井筒内的沿程摩擦阻力和加速度压力损失,引入拟表皮系数表征储层非均质性造成的物性差异.实例计算结果表明,该模型与有限差分数值模拟模型计算结果吻合较好,证实了该方法的可靠性;储层非均质性和沿程压降对水平井产量剖面影响较大,渗透率高的区域,流入量较大;在早期,原油的流动为非稳态时,井筒压降对计算结果影响很大,当水平井较长时,井筒压降对产量影响不可忽略;由于井筒流量从趾端到跟端逐渐增加,井筒压降逐渐增大.

理论反射系数对于完全匹配层边界的吸收效果影响分析

本文基于平面波理论和空间二阶精度差分格式推导出声波方程数值模拟中的完全匹配层边界条件反射系数公式,并基于该公式系统分析了理论反射系数对于完全匹配层吸收效果的影响。实验结果表明,对于小入射角度(小于30°)的入射波,当理论反射系数R取10^(-4)时,完全匹配层有最优的吸收效果;对于入射角度为40°、50°和60°的入射波,当理论反射系数R分别取10^(-5)、10^(-6)和10^(-8)时完全匹配层边界反射系数最小;而对更大角度的入射波,需要更小的理论反射系数R才能使得完全匹配层达到最优的吸收效果。

基于BP神经网络的地下管廊施工质量控制

为了促进工程施工质量前期控制在地下管廊工程中的应用,结合BP神经网络基本理论,提出了一种基于人、材料、机械设备、施工方法和环境五大质量影响因素(即4M1E)的量化处理方法.通过MATLAB R2014a数值仿真模拟软件实现对4M1E的量化处理,建立了地下管廊施工质量前期预测模型,并对该模型结果进行了测试与验证.结果表明,模型中的预测值与期望值基本一致,证明了该模型是有效的、可靠的,进而对地下管廊施工质量前期控制有着重要的参考价值.

特高压直流输电线路塔基边坡的稳定性分析

山区输电线路工程塔基一般修建于自然边坡上,塔基边坡的稳定状态是涉及输电线路工程安全的关键技术问题。以甘肃酒泉—湖南±800 kV特高压直流输电线路工程5535#塔基边坡为例,采用三维有限差分数值模拟方法,利用FLAD 3D软件对塔基和塔基边坡的稳定性进行了分析。结果表明:塔基在荷载作用下,桩顶位置产生了向坡外向下的位移,桩端位置产生了向坡内的位移,且桩水平位移最大值为4.025 mm,处于桩水平变形允许范围内;塔基荷载作用对边坡的应力总体影响不大,局部范围内应力有所增加,且仅在坡顶局部出现拉破坏,坡顶以下坡体处于弹性变形范围,未形成整体变形失稳的破坏区,对边坡的整体稳定性影响较小;建议对塔基边坡坡顶进行适当的加固处理,以满足特高压直流输电线路工程安全运行的要求。

Numerical simulation of intermediate phase growth in Ti/Al alternate foils

To investigate the diffusion reaction between Ti/Al solid diffusion couple, Ti/Al alternate foils formed by hot pressing were annealed at 525, 550, 575 and 600 °C for time ranging from 1 to 40 h. The experimental results show that TiAl3 was the only observed phase at Ti/Al interface. The interface thermodynamics favored the preferential formation of TiAl3 in Ti/Al couple. The growth of TiAl3 layer occurred mainly towards Al foil side and exhibited a parabolic law. Using the interdiffusion coefficients calculated based on the contribution of grain boundary diffusion, the growth of TiAl3 was simulated numerically with the finite difference method, and the simulated results were in good agreement with the experimental ones.

Stability of finite difference numerical simulations of acoustic logging-while-drilling with different perfectly matched layer schemes

In acoustic logging-while-drilling （ALWD） finite difference in time domain （FDTD） simulations, large drill collar occupies, most of the fluid-filled borehole and divides the borehole fluid into two thin fluid columns （radius -27 mm）. Fine grids and large computational models are required to model the thin fluid region between the tool and the formation. As a result, small time step and more iterations are needed, which increases the cumulative numerical error. Furthermore, due to high impedance contrast between the drill collar and fluid in the borehole （the difference is 〉30 times）, the stability and efficiency of the perfectly matched layer （PML） scheme is critical to simulate complicated wave modes accurately. In this paper, we compared four different PML implementations in a staggered grid finite difference in time domain （FDTD） in the ALWD simulation, including field-splitting PML （SPML）, multiaxial PML（M- PML）, non-splitting PML （NPML）, and complex frequency-shifted PML （CFS-PML）. The comparison indicated that NPML and CFS-PML can absorb the guided wave reflection from the computational boundaries more efficiently than SPML and M-PML. For large simulation time, SPML, M-PML, and NPML are numerically unstable. However, the stability of M-PML can be improved further to some extent. Based on the analysis, we proposed that the CFS-PML method is used in FDTD to eliminate the numerical instability and to improve the efficiency of absorption in the PML layers for LWD modeling. The optimal values of CFS-PML parameters in the LWD simulation were investigated based on thousands of 3D simulations. For typical LWD cases, the best maximum value of the quadratic damping profile was obtained using one do. The optimal parameter space for the maximum value of the linear frequency-shifted factor （a0） and the scaling factor （β0） depended on the thickness of the PML layer. For typical formations, if the PML thickness is 10 grid points, the global error can be reduced to 〈1% using the optimal PML parameters, and the error will decrease as the PML thickness increases.

Seismic wavefield modeling in media with fluid-filled fractures and surface topography

We present a finite difference （FD） method for the simulation of seismic wave fields in fractured medium with an irregular （non-fiat） free surface which is beneficial for interpreting exploration data acquired in mountainous regions. Fractures are introduced through the Coates-Schoenberg approach into the FD scheme which leads to local anisotropic properties of the media where fractures are embedded. To implement surface topography, we take advantage of the boundary-conforming grid and map a rectangular grid onto a curved one. We use a stable and explicit second-order accurate finite difference scheme to discretize the elastic wave equations （in a curvilinear coordinate system） in a 2D heterogeneous transversely isotropic medium with a horizontal axis of symmetry （HTI）. Efficiency tests performed by different numerical experiments clearly illustrate the influence of an irregular free surface on seismic wave propagation in fractured media which may be significant to mountain seismic exploration. The tests also illustrate that the scattered waves induced by the tips of the fracture are re-scattered by the features of the free surface topography. The scattered waves provoked by the topography are re-scattered by the fractures, especially Rayleigh wave scattering whose amplitudes are much larger than others and making it very difficult to identify effective information from the fractures.

Application of the double absorbing boundary condition in seismic modeling

We apply the newly proposed double absorbing boundary condition（DABC）（Hagstrom et al., 2014） to solve the boundary reflection problem in seismic finite-difference（FD） modeling. In the DABC scheme, the local high-order absorbing boundary condition is used on two parallel artificial boundaries, and thus double absorption is achieved. Using the general 2D acoustic wave propagation equations as an example, we use the DABC in seismic FD modeling, and discuss the derivation and implementation steps in detail. Compared with the perfectly matched layer（PML）, the complexity decreases, and the stability and fl exibility improve. A homogeneous model and the SEG salt model are selected for numerical experiments. The results show that absorption using the DABC is considerably improved relative to the Clayton–Engquist boundary condition and nearly the same as that in the PML.

Finite-difference numerical modeling with even-order accuracy in two-phase anisotropic media

To improve the accuracy of the conventional finite-difference method, finitedifference numerical modeling methods of any even-order accuracy are recommended. We introduce any even-order accuracy difference schemes of any-order derivatives derived from Taylor series expansion. Then, a finite-difference numerical modeling method with any evenorder accuracy is utilized to simulate seismic wave propagation in two-phase anisotropic media. Results indicate that modeling accuracy improves with the increase of difference accuracy order number. It is essential to find the optimal order number, grid size, and time step to balance modeling precision and computational complexity. Four kinds of waves, static mode in the source point, SV wave cusps, reflection and transmission waves are observed in two-phase anisotropic media through modeling.

特高压直流输电线路塔基边坡的稳定性分析

文章以某±800kV特高压直流输电线路为背景,针对其5535#塔基边坡稳定性展开探讨,为之引入三维有限差分数值模拟的方式,辅以FLAD3D软件,重点针对塔基及其所在区域边坡的稳定性进行模拟与分析。

地表锚杆在大断面浅埋地铁修建中的应用研究

对地表锚杆在大断面浅埋地铁修建中的应用进行了三维有限差分数值模拟研究,研究了不同长度及不同间距条件下锚杆的受力特征及距隧道洞口不同位置处围岩的沉降规律,同时对锚杆在地铁车站应用的工程措施进行了分析,得出了一些有参考价值的结论。

频率-空间域CPML和特征分析法组合边界研究

在地震波场数值模拟过程中,边界反射是影响其模拟结果的一个重要因素。实际地下介质具有各向异性特征,传统的完全匹配层边界(PML)对于小入射角地震波具有良好效果,但该方法并不能有效地吸收低频波和大角度入射波。针对VTI介质边界反射的问题,本文提出在频率-空间域有限差分法数值模拟中采用卷积完全匹配层(CPML)和特征分析法的组合边界条件,并对该组合边界条件进行数值模拟实验和边界反射吸收效果分析,验证所提方法是一种可靠的人工吸收边界条件,能够有效地压制波场模拟过程中产生的边界反射。

Rough interfaces and ultrasonic imaging logging behind casing

Ultrasonic leaky Lamb waves are sensitive to defects and debonding in multilayer media. In this study, we use the finite-difference method to simulate the response of flexural waves in the presence of defects owing to casing corrosion and rough fluctuations at the cement-formation interface. The ultrasonic obliquely incidence could effectively stimulate the flexural waves. The defects owing to casing corrosion change the amplitude of the early- arrival flexural wave, which gradually decrease with increasing defect thickness on the exterior walls and is the lowest when the defect length and wavelength were comparable. The scattering at the defects decreases the energy of flexural waves in the casing that leaks directly to fluids. For rough cement-formation interface, the early-arrival flexural waves do not change, whereas the late-arrival flexural waves have reduced amplitude owing to the scattering at rough interface.

Three-dimensional numerical modeling of fullspace transient electromagnetic responses of water in goaf

The full-space transient electromagnetic response of water-filled goaves in coal mines were numerically modeled. Traditional numerical modeling methods cannot be used to simulate the underground full-space transient electromagnetic field. We used multiple transmitting loops instead of the traditional single transmitting loop to load the transmitting loop into Cartesian grids. We improved the method for calculating the z-component of the magnetic field based on the characteristics of full space. Then, we established the full- space 3D geoelectrical model using geological data for coalmines. In addition, the transient electromagnetic responses of water-filled goaves of variable shape at different locations were simulated by using the finite-difference time-domain （FDTD） method. Moreover, we evaluated the apparent resistivity results. The numerical modeling results suggested that the resistivity differences between the coal seam and its roof and floor greatly affect the distribution of apparent resistivity, resulting in nearly circular contours with the roadway head at the center. The actual distribution of apparent resistivity for different geoelectrical models of water in goaves was consistent with the models. However, when the goal water was located in one side, a false low-resistivity anomaly would appear on the other side owing to the full-space effect but the response was much weaker. Finally, the modeling results were subsequently confirmed by drilling, suggesting that the proposed method was effective.

An improved rotated staggered grid fi nite difference scheme in coal seam

A coal seam is thin compared to the wavelength of seismic waves and usually shows strong anisotropy.It may form special geological formations,such as goafs and collapses,in coal mines.The existence of these formations may lead to instability in numerical simulations of the goaf area in a coal seam.The calculation speed of simulations is always a factor that restricts the development of simulation techniques.To improve the accuracy and effi ciency of seismic numerical simulations of goaf areas,an improved vacuum method has been incorporated into a rotated staggered grid scheme and calculations implemented by combining parallel computing and task parallelism.This ensures that the proposed numerical simulation method can be utilized in a geological model with large differences in elastic parameters among layers and improve the performance of a parallel application by enabling the full use of processor resources to expedite the calculations.We set up anisotropic coal seam models and then analyze numerically the characteristics of synthetic seismograms and snapshots of diff erent goaf areas with or without collapse.The results show that the proposed method can accurately simulate the goaf area and the calculation method can run with a high speed and parallel efficiency.The research will further advance the technology of anisotropic seismic exploration in coal fi elds,provide data for seismic inversion and build a theoretical support for coal mine disaster prediction.

MATLAB fitting for overcurrent relay and a new digital algorithm study

The overcurrent (OC) protection limit is set usually accorging to a OC protection setting table on digital integrated protection equipment in mine explode isolation high voltage (HV) vacuum switch. For digital integrated protection equipment, OC protection setting table must be converted to be a microcomputer algorithm. This paper first intro-duced a method of the fitting OC protection setting table to be OC relay inverse time characteristics equations using MATLAB least square fitting. On the basis of analyzing these fitting equations, a notion, “integral limit rate” was put forward initially and a OC in-verse time digital algorithm was developed. MATLAB simulation results and a digital signal processor (DSP) based digital integrated protection equipment running test indicate that this algorithm has less calculation amount, less taking up memory, high control accuracy, implements the no-grade setting of OC delay values, suits for all kinds of low-middle mi-crocomputer system implementation.

Influence of Surface Geometry of Grating Substrate on Director in Nematic Liquid Crystal Cell

The director in nematic liquid crystal cell with a weak anchoring grating substrate and a strong anchoring planar substrate is relative to the coordinates x and z.The influence of the surface geometry of the grating substrate in the cell on the director profile is numerically simulated using the two-dimensional finite-difference iterative method under the condition of one elastic constant approximation and zero driven voltage.The deepness of groove and the cell gap affect the distribution of director.For the relatively shallow groove and the relatively thick cell gap,the director is only dependent on the coordinate z.For the relatively deep groove and the relatively thin cell gap,the director must be dependent on the two coordinates x and z because of the increased elastic strain energy induced by the grating surface.