Particle shape consideration in numerical simulation of assemblies of irregularly shaped particles

The mechanical behavior of granular materials depends much on the shape of the constituent particles. Therefore appropriate modeling of particle, or grain, shape is quite important. This study employed the method of direct modeling of grain shape (Matsushima & Saomto, 2002), in which, the real shape of a grain is modeled by combining arbitrary number of overlapping circular elements which are connected to each other in a rigid way. Then, accordingly, a discrete-element program is used to simulate the assembly of grains. In order to measure the effects of grain shape on mechanical properties of assembly of grains, three types of grains—high angular grains, medium angular grains and round grains are considered where several biaxial tests are conducted on assemblies with different grain types. The results show that the angularity of grains greatly affects the behavior of granular soil.     

光固化3D打印与传统涂膜法制备聚酰亚胺的摩擦学性能比较研究

为研究光固化3D打印成形技术及其材料配方对光敏聚酰亚胺摩擦学性能的影响,分别采用光固化3D打印技术和传统涂膜成形对比评价了几种光敏型和热固型聚酰亚胺的摩擦学性能、热稳定性及机械性能等.研究表明：为适应光固化3D打印成形需要而加入的活性稀释剂和交联剂对光敏聚酰亚胺的机械性能具有提升作用,但削弱了减摩抗磨和耐热性能;相较于涂膜成形的热固性聚酰亚胺,3D打印样品的耐热性能降低,摩擦系数升高了0.08,磨损率增加了9×10^-6 mm³/(N·m).尽管光固化3D打印聚酰亚胺的减摩抗磨性能低于热固成形聚酰亚胺,但基于光固化3D打印技术的一体成型、高精度和自由制造等诸多优势,对实现高性能及复杂结构精密润滑器件的一体化智能制造具有重要的工程意义.     

求解中短半径弯螺杆钻具的纵横弯曲法

介绍了一种求解中短半径($K=1^\circ$/m$ \sim 3^\circ$/m)弯螺杆 钻具的纵横弯曲法, 以指导弯螺杆钻具的设计和使用. 采用变刚度梁柱理论, 并应用等效载荷法对具有初始结构弯角的梁柱进行等效处理, 根据钻具组合支座连续条件及 边界条件建立了中短半径水平井造斜螺杆钻具组合的力学模型, 进而求得钻头侧向力, 依此 预测弯螺杆钻具的造斜能力. 这种分析方法得到了成功应用.     

隧道洞口段非均质及各向异性土质裂缝仰坡稳定性上限解

针对忽略岩土体非均质和各向异性将导致边坡稳定性评价产生误差的问题,应用极限分析上限理论及抗剪强度系数折减法,推导土体强度非均质和各向异性影响下隧道洞口含裂缝仰坡稳定性解析式,探究土体强度非均质和各向异性对仰坡稳定性系数、坡顶裂缝位置、隧道拱顶失稳范围及仰坡安全系数的影响。结果表明,裂缝深度及坡角越大,仰坡稳定性系数越小;非均质系数越大和各向异性系数越小,维持仰坡稳定的临界坡高越大;非均质系数及各向异性系数越大,裂缝距坡顶边缘越远,隧道拱顶失稳范围越大;非均质系数增大有利于仰坡稳定,而各向异性系数越大仰坡越易失稳。     

地下坑道对其临界震塌爆距处钻地武器爆炸载荷的动力响应

利用非线性显式动力有限元程序,采用多物质流固耦合计算方法,就GBU-28钻地弹在地下坑道临界震塌爆距处爆炸时,对地下直墙拱坑道的动力响应进行数值模拟。根据围岩动力稳定性和混凝土动态强度判据,结合模拟结果,分析衬砌结构与围岩的相互作用。钻地弹在直墙圆拱断面的坑道临界震塌爆距处爆炸时:围岩处于临界破坏状态,但混凝土衬砌结构处于稳定状态;拱顶的应力峰值明显,且柱状装药情况下,爆炸近区的应力较集团装药情况下的大;拱肩位置出现应力集中;围岩与衬砌结构特征位置处的相互作用载荷与对应质点的振动速度相互耦合,基本成对应的关系。     

Nonlinear mechanics of flexible cables in space robotic arms subject to complex physical environment

A nonlinear model of a special cable in space robotic arms is developed in space environment. The mechanic effects of control cables in powerful robots can often be neglected. However, in complex space multi-physics environments, involving ultra-low temperature, radiation, and other extreme conditions of outer space, the externally mounted cables (protected by shielding layers) can induce strong nonlinear interference to robot arms; and this can induce further small-range slow rotations or oscillations of the flexible joint of robots at a specific posture, which consequently affect the precision and operation performance of end effectors. Effective mathematical models on nonlinear mechanics of strong cables under multi-physics environments and their effects on weak robots have not been well developed yet. Complex key factors, such as low gravity, nonlinear friction, and unexpected curved surface constraints, have not been extensively investigated either. In this study, considering all these key factors, a Kirchhoff nonlinear mechanical model of cables in complex space environments is developed, and a relatively improved algorithm based on a trust-region strategy is proposed for solving this nonlinear model, based on which the geometry and terminal force of the modeled robot cable can be obtained. The validity and accuracy of the proposed algorithm and theoretical calculation results are verified via experiments. The theoretical findings revealed in this study are significant to future research on the slow rotations and oscillations of weak robot joints in space exploration with robotic arms.

     

关口垭隧道塌方处理及效果分析

常张高速公路关口垭隧道右洞施工过程中连降暴雨,导致YK73+955~YK73+925段塌方,分析塌方原因后,结合工程具体情况,采用超前小导管预注浆方法处理塌方区,在处理段增设两个监测断面,从隧道收敛位移和拱顶下沉规律结果可知,超前小导管预注浆方法处理塌方区效果良好。     

力敏感受体介导细胞功能调控的力学生物学研究

细胞膜是细胞与外部环境进行物质与能量交换的界面,是调节细胞正常生命活动的重要结构基础.细胞膜上力敏感受体可通过力学作用方式参与并影响细胞的力信号转导等功能.整合素和钙黏素是细胞膜上典型的力敏感受体,可介导细胞与细胞周围基质或邻近细胞发生力学作用,并将力学刺激信号转导为生化信号,进而激活细胞内一系列应答反应,最终影响细胞生长、分化、增殖、凋亡和迁移等功能.力敏感受体介导细胞功能调控研究已成为探索细胞主动响应外界复杂力学微环境的力学生物学机制的关键,为进一步深入认识生理和病理状态下细胞功能变化规律,为揭示疾病的发生、发展机制提供重要的力学生物学理论与实验依据.本文总结了力敏感受体介导细胞功能调控的国内外研究进展;介绍了黏附界面处典型力敏感受体的结构和功能;总结了这些力敏感受体参与的细胞力信号感知与响应的数理模型;概述了细胞通过力敏感受体进行力学信号转导的过程;介绍了黏附介导细胞功能调控的力学生物学过程和机制;简述了体外构建模拟细胞力学微环境中细胞-细胞外基质和细胞-细胞力学相互作用的技术;指出了力敏感受体介导细胞功能调控的力学生物学研究发展趋势和未来方向.     

板结构功率流的参数研究

板以及肋板结构在工程中有着广泛的应用，其振动嗓声问题一直受到理论和工程领域的关注。本文在板结构功率流理论的基础上￣［１］，对板的损耗因子和不同加肋形式对其功率流的影响进行了分析和测量。     

BBD板结构的振动功率流研究

多冲击体阻尼（下文简称ＢＢＤ）是结构振动、噪声控制中的一项新技术。本文基于它的作用机理和机械导纳与弹性结构动力学理论，推导了三种不同ＢＢＤ板结构振动功率流的解析表达式。并进行了数值计算，给出了测量验证结果。最后定量分析了ＢＢＤ对板结构功率流的影响。     

Coupling of discrete-element method and smoothed particle hydrodynamics for liquid-solid flows

Particle based methods can be used for both the simulations of solid and fluid phases in multiphase medium, such as the discrete-element method for solid phase and the smoothed particle hydrodynamics for fluid phase. This paper presents a computational method combining these two methods for solid-liquid medium. The two phases are coupled by using an improved model from a reported Lagrangian-Eulerian method. The technique is verified by simulating liquid-solid flows in a two-dimensional lid-driven cavity.     

基于遗传算法的隧道围岩变形稳定可靠性分析

由于隧道的开挖,隧道围岩的初始应力状态将发生变化,围岩发生卸荷变形,并可能导致隧道的失稳。为了研究隧道开挖后围岩变形的可靠性,建立了隧道围岩变形可靠度指标计算模型,并用遗传算法进行求解。应用本文方法对一高速公路隧道围岩变形的可靠性进行分析。从结果可以看出,围岩的潜在破坏区域出现在拱顶和两侧拱肩区域,从这些区域的可靠度指标和破坏概率值可以看出,该隧道毛洞的拱顶下沉和拱肩收敛可靠度都满足不了规范的要求,要及时进行支护。     

Three-dimensional dynamic model for off-road vehicles using discrete body dynamics

This paper presents a simple, reliable dynamics model of off-road vehicle operation in real-time (RT) on terrain with obstacles. The numerical model was formulated by a new method – DBD (Discrete Body Dynamics). The new method is based on a discrete-element method, where the equations of motion are linear and simple to solve.In this new method, the suspension systems are composed of soft and stiff springs and dampers (instead of suspension arms and joints constrains), to present the kinematics and dynamics of real suspension. Reduction of the number of bodies and avoidance of constraints significantly improves model efficiency and simplicity.The tires–soil interaction was modeled using Brixius prediction. Specific soil properties were obtained from the classification system for each tire–soil interaction, size, and geometric area. The tire–ground contact was determined by topographic surface and adjustment of the forces and direction acting on the tires.The proposed method allows quick and simple definition of a vehicle. The model is written as an independent software infrastructure, enabling easy integration with any other software component.Simulation results were compared with Siemens' VL commercial multibody dynamics program. The performance of the proposed method was very similar to the commercial program (R² > 0.9), with the significant advantage of much higher RT performance.     

A novel numerical scheme for the investigation of surface tension effects on growth and collapse stages of cavitation bubbles

In the present study the effects of surface tension on the growth and collapse stages of cavitation bubbles are studied individually for both spherical and nonspherical bubbles. The Gilmore equation is used to simulate the spherical bubble dynamics by considering mass diffusion and heat transfer. For the collapse stage near a rigid boundary, the Navier–Stokes and energy equations are used to simulate the flow domain, and the VOF method is adopted to track the interface between the gas and the liquid phases. Simulations are divided into two cases. In the first case, the collapse stage alone is considered in both spherical and nonspherical situations with different conditions of bubble radius and surface tension. According to the results, surface tension has no significant effects on the flow pattern and collapse rate. In the second case, both the growth and collapse stages of bubbles with different initial radii and surface tensions are considered. In this case surface tension affects the growth stage considerably and, as a result, the jet velocity and collapse time decrease with increasing surface tension coefficient. This effect is more significant for bubbles with smaller radii.     

高铬铸铁钻井泵缸套之磨损机理与新型缸套的研究

本文对不同地区使用换效的１０只高铬铸铁钻井泵缸套严重磨损表面进行了金相分析、扫描电子显微镜形貌分析和磨屑的铁谱分析，进而对缸套的磨损失效过程和起主导作用的磨损机理作了探讨，提出了具有一定理论价值和实用意义的新观点。文章根据缸套材质的匹配试验结果指出，缸套的含Ｃｒ量以１０％（ｗｔ）左右为最佳，既能保证其具有良好的耐磨性而延长使用寿命，又能减少Ｃｒ的用量而使成本降低１７．８５％。按照本文提供的数据资料     

钢筋混凝土烟囱爆破拆除的下坐及早期断裂预测

为分析钢筋混凝土烟囱在爆破拆除时发生下坐与空中断裂现象的机制并对其进行预测,对一高180 m烟囱的下坐和空中断裂过程进行了观测和分析。基于混凝土的压缩全应力-应变曲线特征,分析了烟囱支撑区的破坏过程,构建了烟囱失稳下坐的判别模型。通过建立烟囱下坐冲击作用下爆破切口以上烟囱的动力响应模型,分析了下坐冲击附加动应变波在烟囱中的传播特征。研究结果表明,考虑混凝土全应力-应变曲线特征和支撑区横截面应力和应变分布特征时,倾覆力矩与抵抗力矩的比值f可作为失稳下坐的判别条件之一;烟囱发生下坐的必要条件是支撑区最小残余承载力小于烟囱的重量。烟囱在下坐结束阶段,获得一定初速度的烟囱冲击基础时将产生冲击荷载,并在烟囱中部引起大于底端应变的应变,即产生动应变高程放大效应,该效应是导致烟囱发生早期断裂的主要原因。烟囱越高,下坐冲击历时越短,动应变高程放大效应越显著,发生断裂的风险也越大。随着烟囱高度的增加,烟囱最危险截面的位置也越高:由烟囱中下部移至烟囱中上部。     

Experimental analysis of propagation of fatigue crack on gears

Gears of different sizes and with different systems of loading are indispensable components of machines and devices. When optimizing such gear assemblies, on of the most important parameters is their required service life. To calculate the service life as precisely and reliably as possible, researchers need to use the required mathematical models for describing loading, the geometry, properties of materials and fracture mechanics parameters. The accuracy and reliability of the gear model assemblies can be compared only with appropriate experimental results. To this end, the authors have used and developed a series of methods and test pieces. A comparison of results has shown that the models and approaches are adequate.     

The structural performance of the periodic truss

Matrix methods of linear algebra are used to analyse the structural mechanics of the periodic pin-jointed truss by application of Bloch's theorem. Periodic collapse mechanisms and periodic states of self-stress are deduced from the four fundamental subspaces of the kinematic and equilibrium matrix for the periodic structure. The methodology developed is then applied to the Kagome lattice and the triangular-triangular (T-T) lattice. Both periodic collapse mechanisms and collapse mechanisms associated with uniform macroscopic straining are determined. It is found that the T-T lattice possesses only macroscopic strain-producing mechanisms, while the Kagome lattice possesses only periodic mechanisms which do not generate macroscopic strain. Consequently, the Kagome lattice can support all macroscopic stress states. The macroscopic stiffness of the Kagome and T-T trusses is obtained from energy considerations. The paper concludes with a classification of collapse mechanisms for periodic lattices.     

Automated Experimental Modal Analysis of Bladed Wheels with an Anthropomorphic Robotic Station

Experimental modal analysis is challenging when the component has a highly three-dimensional shape, since a great number of measurement points are needed with accurate positioning. An anthropomorphic robotic station is proposed to automate this analysis, specifically on bladed wheels. This provides a reliable control of the spot location and of the beam orientation of a Laser Doppler Vibrometer. The modal frequencies were obtained along with the vibrational shapes and their spatial resolution was managed by exploiting the programming flexibility of the robotic station. The SAFE diagram was easily obtained by measuring a single point for each sector, and an extension of this diagram was demonstrated for the splitter blade wheels. The use of multiple measurement points, for each wheel sector, significantly improved the characterization of the modes having the same number of nodal diameters, hence the same shape coordinate on the SAFE diagram.     

三维圆柱型颗粒堆坍塌问题的全相态数值模拟

静态颗粒堆在重力作用下的坍塌问题, 是认识和理解许多人为过程和自然现象的基础. 采用传统方法进行模拟存在单颗粒追踪数量大、宏观模拟流变特性明显和相态演变复杂等计算难点. 本文从颗粒介质表现出不同相态的物理机理出发, 对全相态概念进行了定义并进行了区域划分. 根据颗粒介质的应力-应变关系及体积分数的不同, 通过确定不同相态之间的耦合关系和转化准则, 将描述各相态的现有理论有效结合起来, 建立了描述颗粒介质经历全部相态的耦合模型理论. 采用光滑离散颗粒流体动力学方法和离散单元法相耦合的策略, 对颗粒介质物理模型求解, 实现了对不同长径比下的三维圆柱型颗粒堆坍塌过程的数值模拟. 计算结果与实验结果吻合较好, 同时与离散单元法相比, 计算量得到了控制. 不仅捕捉到了不同参数影响下颗粒堆坍塌后沉积的不同现象, 同时获得了不同条件参数对颗粒堆坍塌后铺展特性的影响规律, 为揭示工业和自然界中广泛存在的颗粒介质复杂运动机理提供有效的支撑.