The Interaction of Oblique Flexural Gravity Waves With a Small Bottom Deformation on a Porous Ocean-Bed： Green＇s Function Approach

The interaction of oblique incident water waves with a small bottom deformation on a porous ocean-bed is examined analytically here within the framework of linear water wave theory. The upper surface of the ocean is assumed to be covered by an infinitely extended thin uniform elastic plate, while the lower surface is bounded by a porous bottom surface having a small deformation. By employing a simplified perturbation analysis, involving a small parameter c^（〈〈l ）, which measures the smallness of the deformation, the governing Boundary Value Problem （BVP） is reduced to a simpler BVP for the first-order correction of the potential function. This BVP is solved using a method based on Green＇s integral theorem with the introduction of suitable Green＇s function to obtain the first-order potential, and this potential function is then utilized to calculate the first-order reflection and transmission coefficients in terms of integrals involving the shape function c（x） representing the bottom deformation. Consideration of a patch of sinusoidal ripples shows that when the quotient of twice the component of the incident field wave number propagating just below the elastic plate and the ripple wave number approaches one, the theory predicts a resonant interaction between the bed and the surface below the elastic plate. Again, for small angles of incidence, the reflected wave energy is more as compared to the other angles of incidence. It is also observed that the reflected wave energy is somewhat sensitive to the changes in the flexural rigidity of the elastic plate, the porosity of the bed and the ripple wave numbers. The main advantage of the present study is that the results for the values of reflection and transmission coefficients obtained are found to satisfy the energy-balance relation almost accurately.

Scattering of Oblique Surface Waves by the Edge of Small Deformation on a Porous Ocean Bed

The scattering of oblique incident surface waves by the edge of a small cylindrical deformation on a porous bed in an ocean of finite depth, is investigated here within the framework of linearized water wave theory. Using perturbation analysis, the corresponding problem governed by modified Helmholtz equation is reduced to a boundary value problem for the first-order correction of the potential function. The first-order potential and, hence, the reflection and transmission coefficients are obtained by a method based on Green＇s integral theorem with the introduction of appropriate Green＇s function. Consideration of a patch of sinusoidal ripples shows that when the quotient of twice the component of the incident field wave number along x-direction and the ripple wave number approaches one, the theory predicts a resonant interaction between the bed and the free-surface, and the reflection coefficient becomes a multiple of the number of ripples. Again, for small angles of incidence, the reflected energy is more as compared to the other angles of incidence. It is also observed that the reflected energy is somewhat sensitive to the changes in the porosity of the ocean bed. From the derived results, the solutions for problems with impermeable ocean bed can be obtained as particular cases.

A Note on the Solution of Water Wave Scattering Problem Involving Small Deformation on a Porous Channel-Bed

The solution of water wave scattering problem involving small deformation on a porous bed in a channel, where the upper surface is bounded above by an infinitely extent rigid horizontal surface, is studied here within the framework of linearized water wave theory. In such a situation, there exists only one mode of waves propagating on the porous surface. A simplified perturbation analysis, involving a small parameter ε （≤1） , which measures the smallness of the deformation, is employed to reduce the governing Boundary Value Problem （BVP） to a simpler BVP for the first-order correction of the potential function. The first-order potential function and, hence, the first-order reflection and transmission coefficients are obtained by the method based on Fourier transform technique as well as Green＇s integral theorem with the introduction of appropriate Green＇s function. Two special examples of bottom deformation： the exponentially damped deformation and the sinusoidal ripple bed, are considered to validate the results. For the particular example of a patch of sinusoidal ripples, the resonant interaction between the bed and the upper surface of the fluid is attained in the neighborhood of a singularity, when the ripples wavenumbers of the bottom deformation become approximately twice the components of the incident field wavenumber along the positive x -direction. Also, the main advantage of the present study is that the results for the values of reflection and transmission coefficients are found to satisfy the energy-balance relation almost accurately.

Incompatible thermal deformation of interlayers and corresponding damage mechanism of high-speed railway track structure

In the service period,the instability of ballastless track bed are mostly related to the damage of interlayers which are mainly resulted from the incompatible thermal deformation of interlayers.The temperature field within the ballastless track bed shows significant non-uniformity due to the large difference in the materials of various structure layers,leading to a considerable difference in the force bearing of different structure layers.Unit Ballastless Track Bed(UBTB)is most significantly affected by temperature gradient.The thermal deformation of interlayers within UBTB follows the trend of ellipsoid-shape buckling under the effect of the temperature gradient,resulting in a variation of the contact relationship between structure layers and a significant periodic irregularity on the rail.When the train travels on the periodically irregular rail,the structure layers are locally contacted,and the contact zone moves with the variation of the wheel position.This wheel-followed local contact greatly magnifies the interlayer stress,causes interlayer damage,and leads to a considerable increase in the bending moment of the track slab.Continuous Ballastless Track Bed(CBTB)is most significantly affected by the overall temperature variation,which may cause damage to the joint in CBTB.Under the combined action of the overall temperature rise and the temperature gradient,the interlayer damage continuously expands,resulting in bonding failure between structural layers.The thermal force in the continuous track slabs will cause the up-heave buckling and the sudden large deformation of the track slab,and the loss of constraint boundary of the horizontal stability.For the design of a ballastless track structure,the change of bearing status and structural damage related to the incompatible thermal deformation of interlayers should be considered.

Several Typical Geomechanical Models of Deformation Fracture of Mountain in High Earthquake Intensity Area

The deformation fracture and stability of mountain under the earthquake action is an important issue that arouses concern of researchers in the field of engineering geology.The authors,from 2000 to 2006, selected the 1933 earthquake in Diexi zone as a typical study site to carry out the genetic mechanism research of mountain deformation-fracture caused by earthquake; in order to have comparability,the breadth

Optimal mining sequence for coal faces under a bedding slope:insight from landslide prevention

Repetitive mining beneath bedding slopes is identified as a critical factor in geomorphic disturbances, especially landslides and surface subsidence. Prior research has largely concentrated on surface deformation in plains due to multi-seam coal mining and the instability of natural bedding slopes, yet the cumulative impact of different mining sequences on bedding slopes has been less explored. This study combines drone surveys and geological data to construct a comprehensive three-dimensional model of bedding slopes. Utilizing FLAC3D and PFC2D models, derived from laboratory experiments, it simulates stress, deformation, and failure dynamics of slopes under various mining sequences. Incorporating fractal dimension analysis, the research evaluates the stability of slopes in relation to different mining sequences. The findings reveal that mining in an upslope direction minimizes disruption to overlying strata. Initiating extraction from lower segments increases tensile-shear stress in coal pillar overburdens, resulting in greater creep deformation towards the downslope than when starting from upper segments, potentially leading to localized landslides and widespread creep deformation in mined-out areas. The downslope upward mining sequence exhibits the least fractal dimensions, indicating minimal disturbance to both strata and surface. While all five mining scenarios maintain good slope stability under normal conditions, recalibrated stability assessments based on fractal dimensions suggest that downslope upward mining offers the highest stability under rainfall, contrasting with the lower stability and potential instability risks of upslope downward mining. These insights are pivotal for mining operations and geological hazard mitigation in multi-seam coal exploitation on bedding slopes.

Micro-structural evolution and their effects on physical properties in different types of tectonically deformed coals

The macromolecular structure of tectonically deformed coals(TDC)may be determined by the deformation mechanisms of coal.Alterations of the macromolecular structure change the pore structure of TDC and thereby impact physical properties such as porosity and permeability.This study focuses on structure and properties of TDC from the Huaibei and Huainan coal mining areas of southern North China.Relationships between the macromolecular structure and the pore structure of TDC were analyzed using techniques such as X-ray diffraction,high-resolution transmission electron microcopy,and the low-temperature nitrogen adsorption.The results indicated that the directional stress condition can cause the arrangement of basic structural units(BSU)more serious and closer.And,the orientation is stronger in ductile deformed coal than in brittle deformed coal.Tectonic deformation directly influences the macromolecular structure of coal and consequently results in dynamic metamorphism.Because the size of BSU in brittle deformed coal increases more slowly than in ductile deformed coal,frictional heating and stress-chemistry of shearing areas might play a more important role,locally altering coal structure under stress,in brittle deformed coal.Strain energy is more significant in increasing the ductile deformation of coal.Furthermore,mesopores account for larger percentage of the nano-scale pore volume in brittle deformed coals,while mesopores volume in ductile deformed coal diminishes rapidly along with an increase in the proportion of micropores and sub-micropores.This research also approved that the deformations of macromolecular structures change nano-scale pore structures,which are very important for gas adsorption and pervasion space for gas.Therefore,the exploration and development potential of coal bed methane is promising for reservoirs that are subjected to a certain degree of brittle deformation(such as schistose structure coal,mortar structure coal and cataclastic structure coal).It also holds promise for TDC resulting from wrinkle structure coal of low ductile deformation and later superimposed by brittle deformation.Other kinds of TDC suffering from strong brittle-ductile and ductile deformation,such as scale structure coal and mylonitic structure coal,are difficult problems to resolve.

Compressive mechanical properties and shape memory effect of NiTi gradient lattice structures fabricated by laser powder bed fusion

Laser additive manufacturing (AM) of lattice structures with light weight, excellent impact resistance, and energy absorption performance is receiving considerable attention in aerospace, transportation, and mechanical equipment application fields. In this study, we designed four gradient lattice structures (GLSs) using the topology optimization method, including the unidirectional GLS, the bi-directional increasing GLS, the bi-directional decreasing GLS and the none-GLS. All GLSs were manufactureed by laser powder bed fusion (LPBF). The uniaxial compression tests and finite element analysis were conducted to investigate the influence of gradient distribution features on deformation modes and energy absorption performance of GLSs. The results showed that, compared with the 45° shear fracture characteristic of the none-GLS, the unidirectional GLS, the bi-directional increasing GLS and the bi-directional decreasing GLS had the characteristics of the layer-by-layer fracture, showing considerably improved energy absorption capacity. The bi-directional increasing GLS showed a unique combination of shear fracture and layer-by-layer fracture, having the optimal energy absorption performance with energy absorption and specific energy absorption of 235.6 J and 9.5 J g-1 at 0.5 strain, respectively. Combined with the shape memory effect of NiTi alloy, multiple compression-heat recovery experiments were carried out to verify the shape memory function of LPBF-processed NiTi GLSs. These findings have potential value for the future design of GLSs and the realization of shape memory function of NiTi components through laser AM.

Non-capacity transport of non-uniform bed load sediment in alluvial rivers

Rivers often witness non-uniform bed load sedim ent transport. For a long tim e, non-uniform bed load transport has been assum ed to be at capacity regime determined exclusively by local flow. Yet whether the capacity assumption for non-uniform bed load transport is justified remains poorly understood. Here, the relative time scale of non-uniform bed load transport is evaluated and non-capacity and capacity models are compared for both aggradation and degradation cases with observed data. As characterized by its relative time scale, the adaptation of non-uniform bed load to capacity regime should be fulfilled quickly. However, changes in the flow and sedim ent inputs from upstream or tributaries hinder the adaptation. Also, the adaptation to capacity regime is size dependent, the finer the sediment size the slower the adaptation is, and vice versa. It is shown that the capacity model may entail considerable errors compared to the non-capacity model. For modelling of non-uniform bed load, non-capacity modelling is recommended, in which the temporal and spatial scales required for adaptation are explicitly appreciated.

RELIABILITY OF TEST LANDS TARGETING IN BED-OF-NAILS STYLE TEST FIXTURE

A systematic, accurate and robust evaluating method for fine pitch printed circuit board （PCB） positioning assessment in testing fixture is developed. Targeting reliability of bed-of-nails tester is successfully evaluated by the 2D pattern transform. Probe offset vector with its Weibull and Gaussian distribution estimates are obtained for further investigation about the causes of misalignment on the basis of a batch tests for same kind of PCBs.

泸州地区深层页岩气水平井套变成因机理探讨

四川盆地南部泸州地区深层页岩气储量丰富,是继长宁、威远等中浅层页岩气之后重要的天然气资源接替领域。但在泸州地区深层页岩气开发过程中水平井套管变形(以下简称套变)频发,对水平井压裂施工产生明显影响,制约了该区深层页岩气的规模建产。业内普遍认为套管变形是地层中的断裂发生滑移并对水平井产生剪切和挤压作用引起的,但基于该理论的套变模型与诸多实测数据不相吻合。为了进一步明确套管变形机理,提高套变的防控效果,以泸203井区18口套管变形水平井为对象,基于多臂井径成像测井,逐个对比套变形态、套变层位以及平面断裂发育情况,建立了断裂滑移和层理面滑移2种地质模型,并分析了2种地质模型下的不同套管变形特征。研究结果表明:(1)断裂滑移诱发的套变具有以下规律,即平面上套变仅出现在水平井与断裂带的交会处;套管的变形长度理论上应在10 m以内;套管的变形程度应呈近似对称关系,中部变形强,向两侧逐渐减弱。(2)该区多数套变不在预测的断裂带内,且部分套变段变形长度与形态不符合断裂滑移的特征。(3)层理面滑移可诱发多个相似的套变,在该机制下套管变形长度等于井筒与滑移面相交的距离,且层理面滑移的垂向分布与地层的页理发育程度一致。(4)层理面滑移与断裂滑移具有相似的力学机理,通过三维莫尔圆可以分析钻井和压裂过程中诱发断裂/层理面滑移的关键参数变化。结论认为,除断裂滑移外,层理面滑移是诱发页岩气水平井套管变形的另一重要机理,该研究成果可为深层页岩气规模效益开发的套变防控提供理论指导。

古建筑压煤开采对斜坡上覆堆积层变形扰动影响研究

针对缓倾顺层斜坡上覆堆积层的采动稳定性与变形机理的研究,特别是从协调地下资源开采与地上文物古建筑安全防护视角出发的研究处在探索阶段。以山西省宝应寺斜坡堆积层为研究对象,基于地表动态监测与地质过程机制分析,结合数值模拟研究了堆积层稳定性与地表裂缝成因机制,并探讨优化了开采方式。研究表明:①长壁式地下开采是引起堆积层变形的诱因,堆积层软弱特性与斜坡软硬互层结构是其变形内因。堆积层下伏基岩变形模式为垂向挤压水平拉张,对堆积层变形具有放大效果,牵动其产生地裂缝。堆积层变形破坏机制为:坡下采空—覆岩弯曲—侧岩倾倒变形—下伏岩层应力集中—牵动拉裂;②堆积层裂缝分布在上坡方向采空区工作面端部附近,平面上近似平行,呈“之”字或锯齿状。地物裂缝较之地表裂缝数量更多、但规模更小,寺院建筑群受隐伏张性地裂缝影响致地基形变造成地面以上结构开裂;停采后监测期内,堆积体变形速率趋于收敛,残余变形消减,由变形移动转为基本稳定;③完全采空后,堆积层表现为以下错为主的拉张变形,剪应变显现,持续开采条件下堆积层变形程度将加剧。下伏基岩最大主应力增量达1080.75%,拉应力集中;④短壁房式开采留设区段煤柱利于减小堆积层变形。研究为认识地下资源开采扰动斜坡上覆堆积层变形破坏与寻求古建筑压煤开采文物保护解决方案提供了参考。

铁路基床底层风积沙填料长期动力稳定性研究

为了研究铁路基床底层风积沙填料的长期动力稳定性,以和若铁路某试验段路基为研究对象,开展现场动力响应试验,试验车速分别为5,20和30 km/h,轴重分别为14.5 t和23.5 t,分析动应力随列车速度、轴重及沿深度的变化规律,基于现场测试和以往动三轴试验成果,将临界动应力和累积塑性变形作为评价参数,分别从动强度和动变形2个方面评价和若铁路基床底层风积沙填料的长期动力稳定性。研究结果表明:1)当列车以不大于30 km/h的速度运行时,车速对基床动应力值的影响很小,但轴重的影响十分显著,不同轴重作用下动应力衰减系数沿深度的变化曲线基本重合,动应力经过基床表层衰减约39.7%,传递至基床底层底面衰减约84.6%。2)在和若铁路基床底层范围内,列车荷载产生的动应力为12.86~53.05 kPa,小于风积沙临界动应力66.02~100.21 kPa,从动强度角度来说,风积沙用作铁路基床底层填料满足长期动力稳定性要求。3)基于基床填料的累积塑性应变模型,采用分层总和法计算了和若铁路基床层的累积塑性变形,结果发现列车荷载作用下基床变形主要集中在第1个月,累积变形量为13.59 mm,小于规范允许的月沉降量25 mm,从动变形角度来说,风积沙用作铁路基床底层填料满足长期动力稳定性要求。研究成果可为沙漠地区路基填料选择及基床结构设计提供参考。

钱塘江河口盐官段混合式丁坝修建对水沙及河床影响的实测研究

钱塘江北岸古海塘堤脚加固工程中,辅助围堰施工的临时性管袋黏土混合式丁坝对工程的顺利进行、提高施工效率起着至关重要的作用,然而目前对其周围水沙运动的研究较少,且缺乏相关实测资料。考虑混合式丁坝修建的动态过程,利用无人机拍摄水流视频结合LSPIV(粒子图像测速)处理技术对丁坝修建前、中、后期周围的流场进行分析,并对丁坝附近的地形进行跟踪测量,同时对不同潮差的水流含沙量进行现场测定。结果表明,丁坝具有改变水流方向,减少水流对河岸冲刷的作用,且丁坝越长,挑流作用越明显,为围堰施工提供了较为平缓的水流条件;混合式丁坝对坝后处的促淤效果明显,且坝后地形变化与含沙量密切相关,潮差越大,水体含沙量越高,丁坝后河床淤积幅度越大,有利于提高围堰的施工效率。研究成果对之后相关物理模型和数值模拟的研究提供数据支持。

考虑侧壁阻力的顺层边坡失稳机制及稳定性评价

侧壁阻力作用下,顺层边坡主滑方向将偏离岩层倾向,其变形及失稳机制具有典型特征。以四川盆地马边河流域某顺层边坡为例,基于其工程地质条件,总结顺层边坡不同变形区域的特征,结合失稳边界条件研究了考虑侧壁阻力的顺层边坡失稳演化机制;最后,对比主滑方向偏离岩层倾向与否的受力差异,分析考虑侧壁阻力的顺层边坡三维稳定性,并研究了各影响因素的作用效应。结果表明:(1)考虑侧壁阻力的顺层边坡变形可划为失稳滑走区、滑坡区和稳定区,滑坡区包含滑动区和蠕滑变形区,滑动区岩体滑动后解体风化为碎、块石土,蠕滑变形区受侧壁阻力影响岩体仅变形拉裂;(2)顺层边坡经岩体劣化和前缘临空后,总体呈下部滑动、中部蠕滑拉裂的顺层临空-后退式破坏;滑动区边界受前缘及侧壁临空控制,长度与侧壁冲沟下切段长度相近;蠕滑变形区部分侧壁由节理面转化为挤压带,侧壁阻力增大,稳定性高于临界失稳状态;受侧壁阻力及滑体厚度控制,蠕滑变形区与稳定区界限处因滑体厚度削薄而拉裂;(3)建立了考虑侧壁阻力的顺层边坡稳定性系数计算式,以及岩层倾角δ、滑面倾角α、主滑方向偏离岩层倾向夹角β三角度间的换算关系式,侧壁摩擦系数和β越大,侧壁阻力越利于顺层边坡稳定。

珠海市南水镇金龙边坡变形破坏特征及稳定性评价

边坡稳定性分析评价是边坡调查评价过程中一个不可或缺的环节。以珠海市金龙边坡为研究对象,分析了边坡的发育特征、影响因素、形成机制。在查明边坡岩土体出露及结构特征基础上,根据典型断面C、ϕ值反演分析及敏感性分析结果,确定金龙边坡岩土体物理力学参数,采用极限平衡法对金龙边坡进行稳定性分析评价。评价结果表明:金龙边坡在天然工况下处于欠稳定状态,在饱和及饱和+地震工况下处于不稳定状态。

顺层偏压挤压性软岩隧道让压预留变形角支护技术研究

针对顺层偏压挤压性软岩隧道的非均匀大变形问题,提出一种基于钢拱架预留变形角的新型让压单元。基于三维精细化建模分析顺层偏压荷载下让压预留变形角支护的承载特性和效果,并应用于中老铁路甘庄隧道,验证新型让压预留变形角支护技术的可行性。研究结果表明:1)顺层偏压荷载下隧道支护结构以弯曲变形为主,传统让压柔性节点在弯矩内力作用下易发生受拉破坏,让压预留变形角能有效释放拱架的弯矩内力,适应更大的弯曲变形;2)顺层偏压荷载作用下,采用让压预留变形角的钢拱架整体应力水平明显降低,拱架整体的承载能力满足强度要求;3)工程现场采用局部扩挖和设置钢拱架让压预留变形角后,隧道变形在断面开挖18 d以后控制在允许范围内,初期支护的应力集中现象减弱,钢拱架主体不再发生弯曲破坏。

层理面强度对层状岩体隧道围岩变形的影响

软弱层理面的存在往往直接决定隧道围岩的稳定性,而不同地域层理面强度具有明显差异性,为了揭示隧道围岩变形对层理面强度的响应规律,采用内聚力模型构建了含零厚度层理面的层状岩体隧道数值模型,结合二次开发的声发射数值模拟方法,精细化分析了层理面强度对隧道围岩变形的影响规律。得到以下研究结果:层理面的存在直接影响二次应力场分布,软弱层理面处产生应力集中现象,引起层理面上下界面处的差异变形,从而导致层理面呈现位错滑移趋势,随着层理面强度的增加变形不协调现象减弱,层理面处损伤程度和声发射能量均变小。同时,层理面的存在加大了隧道围岩的变形值,并且层理面强度越弱变形程度越强。因此,针对不同地域层理面强度特性需针对性地进行隧道围岩支护设计,从而保障隧道的安全施工及稳定运营。

Laser powder bed fusion of high-strength Sc/Zr-modified Al–Mg alloy:phase selection,microstructural/mechanical heterogeneity,and tensile deformation behavior

Laser powder bed fusion(L-PBF)of Sc/Zr-modified Al-based alloys has recently become a promising method for developing a new generation of high-performance Al alloys.To clarify the modification roles of Sc/Zr elements,an Al–4.66Mg–0.48Mn–0.72Sc–0.33Zr(wt.%)alloy was processed using L-PBF.The effect of the local solidification condition of the molten pool on the precipitation behavior of primary Al_(3)(Sc,Zr)was analyzed based on time-dependent nucleation theory.It was found that primary Al_(3)(Sc,Zr)inevitably precipitated at the fusion boundary,while its precipitation could be effectively suppressed in the inner region of the molten pool.This subsequently induced the formation of a heterogeneousα-Al matrix.After direct aging,the heredity of solidification microstructure introduced heterogeneous secondary Al_(3)(Sc,Zr)precipitates withinα-Al matrix.Owing to the inverse relationship between grain boundary strengthening and precipitation strengthening,the direct-aged sample with dual heterogeneous structures exhibited reduced mechanical heterogeneity,resulting in lowered hetero-deformation-induced hardening.The low strain-hardening capability in the direct-aged sample promoted necking instability while inducing a large Lüders elongation,which effectively improved the tensile ductility.

基于内聚力模型数值算法的无砟道床变形与损伤分析

针对高速铁路无砟道床层间黏结数值模拟问题,推导混合断裂模式双线性内聚力模型,提出有限元分析框架下的双线性内聚力模型(CZM)数值算法,通过与有限元软件计算结果对比,验证算法的正确性。基于所提出算法,以内聚力单元模拟层间界面,建立CRTSⅢ型板式无砟道床有限元模型,分析温度梯度荷载作用下结构变形与层间损伤规律。结果表明:所提出CZM数值算法与有限元软件计算结果一致,可以反映内聚力单元在受拉、受剪、受拉剪模式下的力学与损伤特性;在-50~100℃/m温度梯度范围内,正温度梯度荷载作用下轨道板垂向位移可达0509 mm,负温度梯度荷载作用下则可达0409 mm;轨道板与自密实混凝土层层间损伤受正温度梯度影响大,层间损伤萌生于板角并向板中发展,温度梯度为972℃/m时层间黏结局部失效。