Effect of eccentric and inclined loading on the bearing capacity of strip footing placed on rock mass

This paper deals with the bearing capacity determination of strip footing on a rock mass in hilly area by considering the influence of inclined and eccentric loading. Applying the generalized HoekBrown failure criterion, the failure behavior of the rock mass is modeled with the help of the power cone programming in the lower bound finite element limit analysis framework. Using bearing capacity factor(Ns), the change in bearing capacity of the strip footing due to the occurrence of eccentrically inclined loading is presented. The variations of the magnitude of Ns are obtained by examining the effects of the Hoek-Brown rock mass strength parameters(uniaxial compressive strength(sci), disturbance factor(D), rock parameter(mi), and Geological Strength Index(GSI)) in the presence of different magnitudes of eccentricity(e) and inclination angle(λ) with respect to the vertical plane, and presented as design charts. Both the inclined loading modes, i.e., inclination towards the center of strip footing(+λ) and inclination away from the center of strip footing(-λ), are adopted to perform the investigation. In addition, the correlation between the input parameters and the corresponding output is developed by utilizing the artificial neural network(ANN). Additionally, from sensitivity analysis, it is observed that inclination angle(λ) is the most sensitive parameter. For practicing engineers, the obtained design equation and design charts can be beneficial to understand the bearing capacity variation in the existence of eccentrically inclined loading in mountain areas.

Experimental and numerical study of buckling-restrained braces configured with out-of-plane eccentricity under cyclic loading

This study focuses on variations in the hysteretic behavior of buckling-restrained braces(BRBs)configured with or without out-of-plane eccentricity under cyclic loading.Quasi-static experiments and numerical simulations were carried out on concentrically and eccentrically loaded BRB specimens to investigate the mechanical properties,energy dissipation performance,stress distribution,and high-order deformation pattern.The experimental and numerical results showed that compared to the concentrically loaded BRBs,the stiffness,yield force,cumulated plastic ductility(CPD)coefficient,equivalent viscous damping coefficient and energy dissipation decreased,and the yield displacement and compression strength adjustment factor increased for the eccentrically loaded BRBs.With the existence of the out-of-plane eccentricity,the initial yield position changes from the yield segment to the junction between the yield segment and transition segment under a tensile load,while the initial high-order buckling pattern changes from a first-order C-shape to a secondorder S-shape under a compressive load.

The Effect of Core Eccentricity on the Structural Behavior of Concrete Tall Buildings

The main purpose of this paper is to investigate the effect of core eccentricity on the structural behavior of concrete tall buildings.Concrete buildings of 55 floors with plan dimensions 48.0×48.0 m2 were investigated.Three cases of main core locations are studied:centric(A),eccentric by one sixth(B)and one third(C)of building width.The three-dimensional finite element method has been used in conducting structural analysis through ETABS software.Gravity and lateral(wind and seismic)loadings are applied to all building cases.It has been concluded that the core location is the prime parameter governing the structural behavior of tall buildings.Although the first two cases(A,B)have acceptable and similar structural behaviors conforming to code limits,in the third case(C),the building behavior came beyond code limits.The author introduced remedial action by adding two secondary cores in the opposite direction of the main core(C-R)to restore the building behavior to the code limits.The results of this action were satisfactory.

Construction of the Genealogy of Eccentric Monks Based on the Historical Materials of Chan Buddhism in the Song Dynasty--From Enlightened Masters in Chan Buddhism,Sages,to Saints

Regarding the Chan Buddhism lamp records from the Song Dynasty and starting from Jing De Zhuan Deng Lu,the category of“enlightened masters in Chan Buddhism”禪門達者was listed separately,meaning a separate category was established for eccentric monks who pretended to be crazy,had unknown inheritance and miraculous deeds,and were difficult to classify.The following lamp records named this category of eccentric monks as“sages”散聖,or“saints”應化聖賢,which constructed another historical genealogy for the special Chan Buddhism eccentric monks.Moreover,the early lamp records included mostly idiosyncratic mad monks from previous dynasties.Since the Southern Song Dynasty,Chan Buddhism historical materials included many sages from the current dynasty.Therefore,this study mainly examines how the genealogy of Chan Buddhism eccentric monks was constructed in Song Dynasty Chan Buddhism lamp records,including quotations,and organizes the images of eccentric monks in the Song Dynasty,as written in Chan Buddhism historical materials,in order that the meaning of existence of these enlightened masters,sages,saints,etc.,included in the genealogy of Song Dynasty eccentric monks in the history of Chan Buddhism can be reflected.

CFD simulation of hydrodynamics and mixing performance in dual shaft eccentric mixers

This work aims to systematically study hydrodynamics and mixing characteristics of non-Newtonian fluid(carboxyl methyl cellulose,CMC)in dual shaft eccentric mixer.Fluid rheology was described by the power law rheological model.Computational fluid dynamics was employed to simulate the velocity field and shear rate inside the stirred tank.The influence mechanism of the rotational modes,height difference between impellers,impeller eccentricities,and impeller types on the flow field have been well investigated.We studied the performance of different dual-shaft eccentric mixers at the constant power input with its fluid velocity profiles,average shear strain rate,mixing time and mixing energy.The counter-rotation mode shows better mixing performance than co-rotation mode,and greater eccentricity can shorten mixing time on the basis of same stirred condition.To intensify the hydrodynamic interaction between impellers and enhance the overall mixing performance of the dual shaft eccentric mixers,it is critical to have a reasonable combination of impellers and an appropriate spatial position of impellers.

Damage response of conventionally reinforced two-way spanning concrete slab under eccentric impacting drop weight loading

Reinforced concrete(RC)structures are generally designed to carry quasi-static gravity loads through almost indispensable components namely slab,however,it may be subjected to high intense loads induced from the impact of projectiles generated by the tornado,falling construction equipment,and also from accidental explosions during their construction and service lifespan.Impacts due to rock/boulder falls do occur on the structures located especially in hilly areas.Such loadings are not predictable but may cause severe damage to the slab/structure.It stimulates structural engineers and researchers to investigate and understand the dynamic response of RC structures under such impulsive loading.This research work first investigates the performance of 1000×1000×75 mm^(3)conventionally reinforced two-way spanning normal strength concrete slab with only tension reinforcement(0.88%)under the concentric impact load(1035 N)using the finite element method based computer code,ABAQUS/Explicit-v.6.15.The impact load is delivered to the centroid of the slab using a solid-steel cylindroconical impactor(drop weight)with a flat nose of diameter 40 mm,having a total mass of 105 kg released from a fixed height of 2500 mm.Two popular concrete constitutive models in ABAQUS namely;Holmquist-Johnson-Cook(HJC)and Concrete Damage Plasticity(CDP),with strain rate effects as per fib MODEL CODE 2010,are used to model the concrete material behavior to impact loading and to simulate the damage to the slab.The slab response using these two models is analyzed and compared with the impact test results.The strain rate effect on the reinforcing steel bars has been incorporated in the analysis using the Malvar and Crawford(1998)approach.A classical elastoplastic kinematic idealization is considered to model the steel impactor and support system.Results reveal that the HJC model gives a little overestimation of peak displacement,maximum acceleration,and damage of the slab while the predictions given by the CDP model are in reasonable agreement with the experimental test results/observations available in the open literature.Following the validation of the numerical model,analyses have been extended to further investigate the damage response of the slab under eccentric impact loadings.In addition to the concentric location(P1)of the impacting device,five locations on a quarter of the slab i.e.,two along the diagonal(P2&P3),the other two along the mid-span(P4&P5),and the last one(P6)between P3 and P5,covering the entire slab,are considered.Computational results have been discussed and compared,and the evaluation of the most damaging location(s)of the impact is investigated.It has been found that the most critical location of the impact is not the centroid of the slab but the eccentric one with the eccentricity of 1/6th of the span from the centroid along the mid-span section.

Transition from isotropic to polar state of self-driven eccentric disks

Inspired by the eccentricity design of self-driven disks,we propose a computational model to study the remarkable behavior of this kind of active matter via Langevin dynamics simulations.We pay attention to the effect of rotational friction coefficient and rotational noise on the phase behavior.A homogeneous system without rotational noise exhibits a sharp discontinuous transition of orientational order from an isotropic to a polar state with the increase of rotational friction coefficient.When there is rotational noise,the transition becomes continuous.The formation of polar state originates from the effective alignment effect due to the mutual coupling of the positional and orientational degrees of freedom of each disk.The rotational noise could weaken the alignment effect and cause the large spatial density inhomogeneity,while the translational noise homogenizes the system.Our model makes further conceptual progress on how the microscopic interaction among self-driven agents yields effective alignment.

Study of beam divergence and thrust vector eccentricity characteristics of the Hall thruster based on dual Faraday probe array planes and its applications

The accurate knowledge of the thrust vector eccentricity and beam divergence characteristics of Hall thrusters are of significant engineering value for the beneficial integration and successful application of Hall thrusters on spacecraft.For the characteristics of the plume bipolar diffusion due to the annular discharge channel of the Hall thruster,a Gaussian-fitted method for thrust vector deviation angle and beam divergence of Hall thrusters based on dual Faraday probe array planes was proposed in respect of the Hall thruster beam characteristics.The results show that the ratios of the deviation between the maximum and minimum values of the beam divergence angle and the thrust vector eccentricity angle using a Gaussian fit to the optimized Faraday probe dual plane to the mean value are 1.4%and 11.5%,respectively.The optimized thrust vector eccentricity angle obtained has been substantially improved,by approximately 20%.The beam divergence angle calculated using a Gaussian fitting to the optimized Faraday probe dual plane is approximately identical to the non-optimized one.The beam divergence and thrust vector eccentricity angles for different anode mass flow rates were obtained by averaging the beam divergence and thrust vector eccentricity angles calculated by the dual-plane,Gaussian-fitted ion current density method for different cross-sections.The study not only allows for an immediate and effective tool for determining the design of thrust vector adjustment mechanisms of spacecraft with different power Hall thrusters but also for characterizing the 3D spatial distribution of the Hall thruster plume.

Research on the Public Perception of Yangzhou Historical and Cultural Districts Based on Network Review Text Analysis

The historical and cultural districts of a city serve as important cultural heritage and tourism resources.This paper focused on four such districts in Yangzhou and performed semantic analysis on online public comments using ROST CM6 software.According to the high frequency words,attention preference of district site elements,activities and feelings in Yangzhou historical and cultural districts were analyzed.Through the analysis of semantic network and public emotional tendency,the relationship between the protection and utilization of Yangzhou historical and cultural districts and the perception and demand of users were discussed,and some suggestions for the protection,utilization and renewal of historical and cultural districts were put forward.

鄂西—黔南地区下寒武统页岩旋回地层学研究

【目的】鄂西—黔南地区下寒武统富有机质页岩层系是页岩气勘探的重要目标,查明不同地区富有机质页岩层段的等时地层关系及其成因已成为页岩气勘探的关键问题。【方法】通过对鄂西ND1井及黔南HY1井下寒武统测井自然伽马数据的旋回地层学分析,识别出下寒武统主要的天文周期,以文献报道的锆石年龄作为锚点建立了两口井的天文年代标尺,并基于沉积噪音模型恢复了两口井下寒武统时期的相对海平面变化。【结果】ND1井牛蹄塘组36 m和9 m的沉积旋回及HY1井16.6 m和4.0 m的沉积旋回代表了轨道周期405 kyr和100 kyr偏心率;ND1井牛蹄塘组和HY1井九门冲组持续时间分别为3.30 Myr和2.64 Myr。给出两种方案的天文年代标尺,方案一以ND1井牛蹄塘组顶作为锚点起点,对应的天文年代标尺年龄区间处于535.20±1.70 Ma~538.50±1.70 Ma;方案二以HY1井九门冲组顶作为锚点起点,对应的天文年代标尺年龄区间处于535.20±1.70 Ma~537.84±1.70 Ma。经过对比分析,两口井海平面变化对应于1.20 Myr旋回和两个三级层序(SQ1和SQ2)。将下寒武统富有机质页岩总有机碳(Total Organic Carbon,TOC)含量和405 kyr旋回滤波及海平面变化曲线对比,结果显示TOC高值段对应于405 kyr旋回最大值,而ND1井TOC低值段对应于两个405 kyr旋回之间的低值。此外,TOC高值段既对应于海平面较高时期,也对应于海平面较低时期。【结论】由于太阳系的混沌行为,无法准确预测寒武纪早期理论轨道偏心率对富有机质页岩驱动的机制。假设偏心率最大值和总有机碳含量最大值对应,则更长的时间段内强季节性变化在某种程度上触发了黑色页岩的富集。此外,相对海平面变化和总有机碳含量对比表明海平面变化和有机质富集不具有因果关系。

渤海湾盆地沾化凹陷古近系沙三下亚段旋回地层学分析及地层划分

湖相细粒沉积多具有连续性,能记录和保存显著的天文旋回信号,是进行天文旋回分析的理想地层。通过对渤海湾盆地沾化凹陷重点井沙三下亚段自然伽马数据进行MTM频谱分析和FFT进化谐波分析,建立了“浮动”天文年代标尺,并在单井上进行了天文旋回地层划分及连井地层对比,为全区搭建了地层格架。研究结果表明:(1)渤海湾盆地沾化凹陷沙三下亚段记录了显著的天文旋回信号,匹配出最优沉积速率为9.0×103cm/Ma;由长偏心率、短偏心率、斜率和岁差周期产生的旋回地层厚度分别为42.3 m,9.0 m,2.4~4.7 m和1.3~1.9 m;(2)沙三下亚段比较稳定的记录了6个长偏心率旋回、25个短偏心率旋回,可将短偏心率曲线作为地层划分依据来进行高精度地层对比。(3)运用天文旋回理论进行岩相发育规律、岩相空间配置关系的预测,可为湖盆沉积中心页岩油气地质“甜点”的精细勘探提供依据。

天体轨道参数调控柴达木盆地第四纪盐类资源形成的新模式

盐类资源的形成受沉积盆地、干旱气候和物源补给三个关键因素的控制,以往的研究主要关注构造、沉积环境和物源因素在成盐过程中的作用,而忽视了干旱和极端干旱气候这一关键因素及其与盆地盐层形成的耦合机制。本文以中德联合在柴达木盆地西部察汗斯拉图凹陷获取的科学深钻为例,运用磁学、元素和同位素地球化学等指标反演研究区的水文气候演化历史,并通过时间域、频率域以及系统动力学演化特征等综合分析手段探究了深时气候变化的控盐机制和规律。结果表明,柴达木盆地西部地区自2.7 Ma以来存在2.2~1.95 Ma、1.3~1.1 Ma、0.85~0.65 Ma和0.5~0.3 Ma四次关键的干旱化加剧和盐层发育期;发现在天体轨道倾角低幅和低偏心率值的同步期,会通过促进北半球冰盖扩张调控北半球中高纬西风环流的位置和强度,进而影响柴达木盆地的气候和水文循环,控制盆地内干旱事件的发生和盐层发育。在轨道-亚轨道-千年尺度上,全球冰量和北半球高纬气候变化也显著地控制了柴达木盆地的干旱事件和盐层发育。柴达木盆地多个凹陷区的盐层对比结果进一步表明,这一天体轨道特殊组合控制盆地的干旱事件和盐层发育过程的机制在全盆地具有普适性,促使柴达木盆地多个不同凹陷区尽管盐层发育存在一些差异,但其主要的盐层发育期均集中在上述四个关键时期。研究成果不仅为柴达木盆地乃至其他干旱区的成盐机制和深时发育规律提供了新的理论视角和研究思路,而且为未来结合构造-气候-物源耦合研究,对不同区域盐类资源发育类型和规律进行精细化研究,以及深入探索深时盐层发育规律提供了重要的研究基础。

偏心效应下大范围转动弹性梁振动特性分析

计及转子偏心效应,借助转子动力学理论,应用Galerkin法和Hamilton原理建立电机-弹性梁系统动力学模型;采用Runge-Kutta法实现动力学解耦,解析不同速度下大范围转动弹性梁的动力学特性,对比分析电机转子动偏心、静偏心与转动梁振动特性的耦合关系。研究结果表明:转子动偏心与系统动力学响应呈现强耦合,动偏心距达到0.5 mm时,转动梁振幅高达2 mm;而静偏心距由0 mm增至0.5 mm时,其振幅均为0.178 mm,后续研究可忽略静偏心因素;随着角速度提高至150 rad/s时,在转子动偏心的作用下,弹性梁振动由周期振动变为非周期振动,也是该类机构高速下呈现不同程度的突发性或间歇性振动的主要原因之一。

炮孔间距对偏心不耦合装药贯通裂纹扩展的影响

为研究光面爆破中偏心不耦合装药炮孔间距对贯通裂纹扩展的影响,利用同心不耦合装药的孔壁压力计算公式并结合应力波叠加原理,推导偏心不耦合装药的炮孔间距计算方法。基于求得的炮孔间距范围,计算3种岩石介质在不同炮孔间距条件下贯通裂纹的扩展位置,并选择砂岩材料进行数值模拟。结果表明:偏心不耦合装药爆破中,贯通裂纹主要集中于偏心侧;抗拉强度大的岩石,贯通裂纹偏离炮孔连心线的程度也较大。砂岩的炮孔间距为60 cm时,贯通裂纹扩展方向与炮孔连心线重合,连心线下方出现裂纹比较集中的贯通区域;炮孔间距的增大导致贯通裂纹远离炮孔连心线,从而造成欠挖。偏心不耦合装药爆破后,偏心侧岩石的损伤明显大于非偏心侧。

倾斜矿体采空区非对称顶板-矿柱结构体协同承载机理

为解决倾斜矿体回采后大倾角顶板和非对称空区可能引发的采空区支撑结构体变形及破坏失稳问题,以某石灰石矿非对称顶板-矿柱支撑结构体为研究对象,构建结构体承载力学模型,求解顶板挠曲变形值及矿柱安全系数,分析不同倾角、跨度比下顶板变形特征及矿柱失稳破坏模式,研究其协同承载机理。结果表明:顶板变形、矿柱失稳破坏模式受采空区倾角θ和跨度比λ的双重影响,顶板变形大小随着θ的增加表现为双增长率,与λ的关系伴随着θ的变化而变化。矿柱失稳破坏模式受θ的影响程度随着λ的增加而减小,当0°<θ≤30°时,矿柱主要为小偏心受压破坏;当θ=0°和30°<θ≤60°时,随着λ值的增加,矿柱破坏模式从大偏心受压破坏向小偏心受压破坏转变。顶板维系采空区稳定的能力随着θ的增加逐渐降低,矿柱维系采空区稳定的最优λ值随着θ的增加逐渐减小,矿柱约束顶板变形作用大小随着λ的增加而降低。数值模拟和工程实例验证了理论计算结果的可靠性,为地下空场法矿山安全开采提供一定的理论支撑。

轴径向静态偏心故障下外转子永磁发电机电磁转矩特性分析

对外转子永磁发电机轴径向静态偏心故障下的电磁转矩特性进行了理论解析、仿真计算和实验验证。首先,在考虑齿槽效应影响条件下,引入磁导修正系数ε(θ),推导出轴径向静态偏心前后气隙磁密表达式,并考虑绕组分布情况,构建一种新型的永磁发电机轴径向静态偏心故障下相电流数学模型,在此基础上得到轴径向偏心下电磁转矩解析表达式。其次,通过有限元仿真计算得到外转子永磁发电机轴径向静态偏心下的电磁转矩波动特性。最后,在一台外转子永磁发电机上通过故障模拟实验实例印证了解析分析和仿真计算结果。结果表明:相较于正常情况,径向偏心时,电磁转矩以直流、二倍频、四倍频成分为主,随着偏心程度的加剧,电磁转矩的直流、二倍频、四倍频成分幅值将随着增大;轴向偏心时,电磁转矩谐波成分不变,随着偏心程度的加剧,各谐波成分幅值将随着减小。对外转子永磁发电机气隙偏心故障分析的一个重要补充,对此类问题的现场检测和鉴定具有参考价值。

斜盘偏距与交错角对飞机液压柱塞泵运动特性影响分析

飞机上常用的直轴式恒压变量液压柱塞泵,出于降低脉动以及改善高频运动时的稳定性需要,斜盘通常设计有偏心距和交错角。针对存在斜盘偏距和交错角的液压柱塞泵,提出了一种能够综合考虑斜盘偏距、交错角、斜盘倾角及斜盘转动速度的柱塞和滑靴运动特性分析方法。以某型航空液压柱塞泵为对象,对比分析了不同偏心距和交错角情况下柱塞的位移、速度特性,以及滑靴在斜盘平面的运动轨迹。按照液压泵配流盘闭死区设计通用准则确定了配流盘闭死区,对柱塞在闭死区内的运动特性进行了分析,结果表明闭死区内柱塞的运动特性深刻影响液压柱塞泵的输出流量和压力脉动。提出的分析方法能够描述斜盘转动(流量切换)过程中的运动动态特性,具有计算效率高、结果准确度高等特点,可用于液压柱塞泵以降低脉动为目标的设计优化。

横向磁通永磁直线电机电磁振动特性分析

横向磁通永磁直线电机的电负荷与磁负荷相互解耦,且各相之间相互解耦,易于实现模块化和多相化,因此在石油开采领域有着良好的应用前景。首先,该文基于磁场调制原理,对横向磁通永磁直线电机的径向电磁力波进行了推导计算,得出对径向电磁力波影响最大的因素为轴向气隙磁通密度分量与径向气隙磁通密度分量,在此基础上对径向电磁力波的时空特性与频谱特性进行仿真计算,得出电枢磁通密度对电机径向电磁力波的频谱特性的影响;然后,考虑到电机实际运行中可能出现的次级偏心问题,揭示偏心度的大小对径向电磁力波幅值的影响,并对比不同偏心度下的电机径向磁拉力与轴向磁拉力,定量分析偏心度对不平衡磁拉力的影响;最后,为避免共振,利用有限元软件对电机的初级进行了模态分析与谐响应分析,结果表明低速状态下横向磁通永磁直线电机的额定运行频率较低,不会引起初级的共振,适合用作往复式潜油电泵的驱动电机。

随钻电成像仪器磁流激励仿真和图像增强方法

提出采用磁流替代环形线圈激励源方法模拟随钻电成像仪器(REIT)响应,在考察随钻电成像测井仪器的探测特性基础上进行环境校正方法研究,旨在获得清晰度增强图像。考虑偏心距、地层电性参数、井眼参数变化,建立仪器响应函数库,利用查库方法反演偏心距并对图像进行井眼环境校正和软件聚集增强处理,实现提高图像质量目的。结果表明,采用本文给出的方法可以对仪器原始采集的电信号进行井眼环境校正和图像增强,对提高图像质量、消除井眼环境对测量影响具有良好效果,在成像测井地层评价、随钻电成像地质导向应用中都具有重要意义。

基于天文周期等时格架预测细粒沉积岩相展布——以鄂尔多斯盆地富县地区三叠系长7段为例

预测陆相不同类型岩相厚度分布是陆相页岩油富集区带优选评价的基础工作,以此开展的不同类型岩相含油条件、储集条件以及可动条件的研究,对靶区优选和水平井段方向部署有着重要的作用。以岩心观察与测井判识为基础,开展测井资料的频谱分析,引入稳定的天文轨道时间周期,进行时空调谐,建立钻井对比的高频层序等时格架,定量计算每个层序旋回内不同类型岩相厚度的平面变化趋势,认识岩相展布规律。针对鄂尔多斯盆地南部富县地区三叠系延长组7段的研究表明,自然伽马测井曲线包括了若干组天文周期信息,其中可以识别出6个完整的稳定405 kyr长偏心率天文周期旋回,以R203井长7段全岩心段观察和测井相特征分析为基础,合理建立高频等时格架进行井间对比。结果表明,泥页岩和纹层页岩主要发育长7_(3)亚段到长7_(2)亚段的底部旋回地层,细砂岩、粉砂岩在长7_(2)亚段中上部到长7_(1)亚段底部的Ⅳ—Ⅴ旋回地层中最为发育;井间横向对比表明,早期旋回的泥页岩和纹层页岩岩相广泛分布,旋回Ⅰ时期主要分布在研究区西南部,旋回Ⅱ时期分布在西部和东—东北部,中部地区局部较厚,而Ⅳ—Ⅴ旋回地层的细砂岩厚度分布由北东—南西的沉积体系控制,平面上呈北—北东往南—南西展布,往西南延伸到ZF27—ZF32井一线,形成了长7段3种源储组合类型。其中纹层页岩与细砂岩岩相配置组合为长7_(3)亚段中上部与长7_(2)亚段中上部—长7_(1)亚段下部层系组合,平面上主要分布在富县地区的中部—北、北东部;页岩岩相厚度发育较好的为长7_(3)亚段,平面上主要分布在富县地区的北东—东部、西南部区域。