THE ANALYSES OF THE THREE-DIMENSIONAL STRESS STRUCTURE NEAR THE CRACK TIP OF MODE I CT SPECIMENS IN ELASTICPLASTIC STATE(Ⅰ)--THE ANALYSES OF CONSTRAINT PARAMETERS AND FRACTURE PARAMETERS

In the present paper,three dimensional analyses of some general constraint parameters and fracture parameters near the crack tip of Mode I CT specimens in two different thicknesses are carried out by employing ADINA program.The results reveal that the constraints along the thickness direction are obviously separated into two parts:the keeping similar high constraint field(Z_(1))and rapid reducing constraints one(Z_(2)).The two fields are experimentally confiremed to correspond to the smooth region and the shear lip on the fracture face respectively.So the three dimensional stress structure of Mode I specimens can be derived through discussing the two fields respectively.The distribution of the Crack Tip Opening Displacement(CTOD)along the thickness direction and the three dimensional distribution of the void growth ratio(V_(g))near the crack tip are also obtained.The two fracture parameters are in similar trends along the thickness direction,and both of them can reflect the effect of thickness and that of the loading level to a certain degree.

Dynamics and Wheel's Slip Ratio of a Wheel-legged Robot in Wheeled Motion Considering the Change of Height

The existing research on dynamics and slip ratio of wheeled mobile robot （WMR） are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS- Ⅱ. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS- Ⅱ in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified, Moreover, the relative horizontal motion between fore/hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore/hind wheels become larger/smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.

Modeling of Fatigue Crack Growth Closure Considering the Integrative Effect of Cyclic Stress Ratio,Specimen Thickness and Poisson's Ratio

Key components of large structures in aeronautics industry are required to be made light and have long enough fatigue lives.It is of vital importance to estimate the fatigue life of these structures accurately.Since the FCG process is affected by various factors,no universal model exists due to the complexity of the mechanisms.Most of the existing models are obtained by fitting the experimental data and could hardly describe the integrative effect of most existing factors simultaneously.In order to account for the integrative effect of specimen parameters,material property and loading conditions on FCG process,a new model named integrative influence factor model（IIF） is proposed based on the plasticity-induced crack closure theory.Accordingly to the predictions of crack opening ratio（γ） and effective stress intensity factor range ratio（U） with different material under various loading conditions,predictions of γ and U by the IIF model are completely identical to the theoretical results from the plane stress state to the plane strain state when Poisson＇s ratio equals 1/3.When Poisson＇s ratio equals 0.3,predictions of γ and U by the IIF model are larger than the predictions by the existing model,and more close to the theoretical results.In addition,it describes the influence of R ratios on γ and U effectively in the whole region from-1.0 to 1.0.Moreover,several sets of test data of FCG rates in 5 kinds of aluminum alloys with various specimen thicknesses under different loading conditions are used to validate the IIF model,most of the test data are situated on the predicted curves or between the two curves that represent the specimen with different thicknesses under the same stress ratio.Some of the test data slightly departure from the predictions by the IIF model due to the surface roughness and errors in measurement.Besides,based on the analysis of the physical rule of crack opening ratios,a relative thickness of specimen is defined to describe the influence of material property,specimen thickness and so forth on FCG characteristics conveniently.In conclusion,the relative thickness of specimen simplifies the expression of FCG characteristic and provides a general parameter to analyze the fatigue characteristics of different materials with various thicknesses under different loading conditions.The IIF model describes the integrative effect of existing influence factors explicitly and quantitatively,and provides a helpful tool for fatigue property estimation of practical component and experiment design.

CONSTRAINTS ON THE CRACK TIP PLASTIC FIELDS UNDER LARGE SCALE YIELD

Plane strain elastic-plastic finite element analyses are used tostudy the stress, strain fields around a straight crack in powerhardening plastic material. Center crack panel (CCP), single edgecrack panel (SECP) and double edge crack panel (DECP) tensionspecimens are analyzed with various crack lengths. Two localconstraint parameters, i.e. in-plane stress ratio T_x andout-of-plane constraint T_z are an- alyzed, which are defined astangential stress dividing normal (open) stress and out-of-planestress dividing the sum of tangential stress and normal stressrespectively.

A review of the effect of a/W ratio on fracture toughness (Ⅲ)——theoretical analysis

In part I and II of this series, experimental investigation in both EPFM and LEFM had been discussed. In this part, further theoretical analysis is given. The theoretical development of Two Parameter Fracture Mechanics by Hancock etc, has rationalized our experimental results. This method can be applied to engineering practice, and will allow the advantage of enhanced toughness for specimens with low levels of constraint to be taken into account for defect assessment.

An Exact Virtual Network Embedding Algorithm Based on Integer Linear Programming for Virtual Network Request with Location Constraint

Network virtualization is known as a promising technology to tackle the ossification of current Internet and will play an important role in the future network area. Virtual network embedding(VNE) is a key issue in network virtualization. VNE is NP-hard and former VNE algorithms are mostly heuristic in the literature.VNE exact algorithms have been developed in recent years. However, the constraints of exact VNE are only node capacity and link bandwidth.Based on these, this paper presents an exact VNE algorithm, ILP-LC, which is based on Integer Linear Programming(ILP), for embedding virtual network request with location constraints. This novel algorithm is aiming at mapping virtual network request(VNR) successfully as many as possible and consuming less substrate resources.The topology of each VNR is randomly generated by Waxman model. Simulation results show that the proposed ILP-LC algorithm outperforms the typical heuristic algorithms in terms of the VNR acceptance ratio, at least 15%.

Dynamic Trajectory Planning of Autonomous Lane Change at Medium and Low Speeds Based on Elastic Soft Constraint of the Safety Domain

Most current research on the trajectory planning of the autonomous lane change focuses on high-speed scenarios and assumes that the states of the surrounding vehicles keep stable during the lane change.The methods based on geometric-curve are mostly used for trajectory planning.In this paper,considering the inevitable development of the autonomous driving,the surrounding vehicles are assumed to be driven by human drivers,while the ego vehicles are able to autonomously change lanes.Representative local lane-change scenarios are then designed and analyzed in detail aiming at medium-and low-speed lane-change conditions.Additionally,in contrast with most research,dynamic trajectory planning which considers the possible state variations of the surrounding vehicles and the driver characteristics is studied and described by a fifth-order polynomial function.The safety and comfort of the dynamic trajectory planning are validated through simulation.Moreover,the elastic soft constraint of the safety domain is designed,whereby the sensitivity of the studied dynamic trajectory planning system is reduced under the premise of ensuring safety.The effectiveness of the elastic soft constraint in terms of improving comfort during the lane change is verified through simulation.The availability of the dynamic trajectory planning system with the elastic soft constraint is demonstrated with the addition of trajectory tracking based on model predictive control,showing its potential in practical applications.

Constrained circular-patch-based texture synthesis

Texture synthesis has been developed for several years.The traditional technique can generate a larger image from a small image while avoid feeling of repetition or uncontinuity.Some constrained synthesis methods which can synthesize image according to special location demand or other demands have been also proposed in recent years.However,in general,these constrained texture synthesis methods are simple and have few controllable factors to meet user＇s diverse needs.To control multiple-sample texture synthesis more flexibly in various aspects such as synthesis location,proportion and semantic objects,we present an interactive texture synthesis approach based on circular patches and constrained by objects according to a certain ratio.With this approach,source exemplars and the target image are firstly divided into several regions with different characters.Users can click the blocks in the source exemplars and the want-to-be-synthesized region in the target image,and then texture in the target image is synthesized with the corresponding regions in the source exemplars.In the process of texture synthesis,circular patch instead of square patch is used to eliminate the aliasing phenomena.Images are synthesized from multiple sample images with ratio constraint and experiments on images show that our approach can get effective results of ratio-constrained multi-sample synthesis.

高桥隧比条件下桥隧相连的隧道洞口联络道设计探讨——以重庆巫溪至陕西镇坪高速公路为例

为确定高桥隧比条件下高速公路桥隧相连的特长隧道洞口联络道的转换长度和结构形式,采用数值模拟方法,选用18.1 m的长头铰接列车为典型车辆,针对10 m~30 m五种左右幅间距及0°~45°四种行驶转换角度,模拟车辆行驶轨迹并计算联络道通行的最小长度。结果表明:1)在满足转换车道基本长度的前提下,模拟隧道洞口联络道推荐长度采用30 m或40 m;2)基于模拟结果推荐的联络道长度,为超高桥隧比的巫镇高速隧道洞口联络道设计提供了重要的基础依据;3)在运营期间,该高速的洞口联络道实现了养护维修或异常工况下的交通转换,有效提升了道路防灾减灾和运营养护能力,为类似工程的设计提供了有益参考。

数字金融、融资约束与企业资本劳动比

文章以2011—2021年中国沪深A股上市企业为研究样本,深入剖析了数字金融对企业资本劳动比的影响、作用机制以及异质性。研究发现,数字金融能够显著提升企业资本劳动比。机制分析发现,数字金融通过缓解融资约束有效提升企业资本劳动比。异质性检验发现,数字金融对企业资本劳动比的影响因数字金融结构、企业内部特征与外部环境的差异而存在异质性,具体为数字金融覆盖广度能够显著提升企业资本劳动比,数字化程度对企业资本劳动比的影响呈显著的正“U”型曲线,使用深度的影响不显著;数字金融对小规模企业、非国有企业、劳动密集型行业企业、非衰退期企业、东部地区企业以及市场化水平较高地区企业资本劳动比提升的促进作用更显著。对此,提出优化数字金融发展环境,引导企业利用数字金融提升资本劳动比,营造公平竞争的市场环境促进企业健康发展的建议。

输电塔斜材不同节点型式下的受压承载力

为研究节点约束下输电塔斜材受压承载力的计算方法,通过对120根等边角钢的偏心受压承载力试验,分析其最小轴、平行轴布置时的破坏模式、承载力及变形形态,研究不同约束刚度、节点型式对其承载力的影响;结合现行行标公式,针对不同节点连接型式(A、B、C类),提出输电塔斜材受压长细比的计算公式.研究结果表明:长细比小于120时,构件承载力主要受偏心控制,偏心越大,承载力越低;而长细比大于120时,构件承载力主要受约束刚度控制,约束刚度越大,承载力越高;A、C类连接在不同长细比时各具优势,但B类连接的承载力始终低于A、C类连接;国内外规范计算值与试验值均存在较大的偏差,具有一定的局限性,体现在小长细比构件偏心及大长细比构件约束修正不足等方面;所提出长细比修正公式的计算结果与试验结果吻合良好,可用于指导工程设计.

基于IAGA的多行设施布局优化方法

针对横向和纵向通道位置和数量均不确定的多行设施布局问题,提出一种基于IAGA的多行设施布局优化方法。考虑设施最大纵横比约束,建立以物流成本、搬运设备空载成本及占地面积成本的加权平均值最小化为优化目标的布局优化模型;设计基于柔性隔间结构编码的改进自适应遗传算法(IAGA)对模型进行求解。算法中设计了自适应调整交叉概率、自适应选择交叉算子(双点交叉算子和单亲单点交换算子)及分别针对隔间结构和设施编号排列的基本位变异算子,提高了其收敛速度和搜索能力。最后,通过案例分析验证了IAGA算法的有效性。

基于分式二次规划的互模糊函数赋形方法

在开展认知雷达波形设计时,由于发射波形与接收滤波器的非匹配体制,互模糊函数赋形相比传统模糊函数赋形优化自由度更高。该文针对强杂波条件下微弱运动目标检测问题,以最大化信干噪比为优化准则,提出了一种联合发射相位编码序列与接收滤波器设计的互模糊函数赋形方法。在恒模约束下,优化问题被建模为二次分式规划形式;然后通过引入辅助变量,并利用共轭梯度法求解Stiefel流形空间上的最小化问题,非凸优化据此转化为恒模约束二次优化问题;通过交替循环和类幂迭代算法求得最优解。此外考虑到发射波形受硬件限制而难以实现严格恒模,该文构建了一种低峰均比约束二次优化问题模型,并利用最近邻向量法求得最优解。最后,不同参数下的仿真与实测数据实验表明,该文赋形方法相较于传统方法具有较高的信干噪比增益和收敛速度。

企业杠杆率如何影响数字化转型?

如何驱动数字化转型成为当下推动经济高质量发展的重要课题。选取2010—2021年A股上市企业作为研究对象,检验企业杠杆率对数字化转型的影响关系、作用机制及作用边界,并拓展分析不同条件下企业杠杆率对数字化转型的差异性影响。研究结果表明:企业杠杆率显著抑制数字化转型,且在控制内生性问题与稳健性检验后结果仍成立。机制检验结果表明:融资约束和研发投入在企业杠杆率与数字化转型之间起部分中介作用。调节效应表明:管理层能力与环境不确定性均负向调节企业杠杆率与数字化转型的关系。拓展性分析结果发现:企业杠杆率对数字化转型的抑制作用在非国有企业、非高科技企业、两职分离与非四大会计师事务所审计的企业中更加显著。企业应寻求内部杠杆水平的最优均衡点,提高资源获取与配置能力;提升内部治理水平与外部环境应对能力,缓解杠杆率对数字化转型的抑制作用;政府部门应完善监督管理措施,以防范化解金融风险。

基于级数展开的位置误差加权定位方法

随着对海洋探索的愈加深入,对水下目标探测能力的要求也愈发严格。针对噪声干扰严重时算法性能大幅度下降的问题,文章主要研究仅利用分布式矢量水听器的波达方向信息对未知目标进行融合定位。在已有的基于位置误差加权方法的基础上,利用几何二次约束减小波达方位角量测误差,并结合泰勒级数展开,将一阶权值推导至高阶,解决在低信噪比情况下定位精度差的问题。仿真结果表明:相对于传统的基于方差倒数的自适应加权算法,该方法在定位精度上有很大提高,尤其在低信噪比的情况下效果显著。

不同风光水配比下多类型电源打捆直流外送系统的功率传输能力研究

风光水打捆经电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)外送系统中,风光水配比不同会影响系统的功率传输能力。文章首先建立风光水打捆直流外送系统的稳态数学模型和状态空间模型,然后提出综合考虑稳态运行约束条件和小信号稳定性约束条件的系统功率传输能力计算方法及流程,掌握不同功率水平下系统稳定运行区域及边界的变化特征,最终得到不同水电出力下的直流外送系统功率传输范围、特定传输功率下所允许的水电出力最小值、风光配比与小信号稳定性的定量关系。通过该方法定量评估风光水配比不同时直流外送系统的功率传输能力,从而优化选取风光水配比。结果表明,水电出力较小时,系统传输功率上限受小信号稳定性制约,下限受电压偏移约束制约;水电出力较大时,系统传输功率上限受LCC-HVDC安全运行约束制约,下限受逆变侧电压偏移、系统潮流约束制约;在功率运行点不变时,风光配比平衡工况系统更加稳定。最后,通过PSCAD/EMTDC下的电磁暂态仿真,验证上述功率传输能力理论计算的正确性。

考虑配电变压器变比误差的配电网多断面联合状态估计

量测配置薄弱一直是困扰配电网状态估计精度的重要原因。台区智能融合终端的广泛应用丰富了量测配置,并使配电网状态估计范围延伸到配电变压器低压侧,客观上对配电变压器参数的准确性提出了更高的要求。配电变压器数量多,参数维护工作量大,参数准确性目前仍难以得到有效保证,变比参数错误是导致配电网状态估计精度低的关键因素。利用配电变压器普遍采用无载调压抽头、变比变化频率较低的特点,提出考虑配电变压器变比误差的配电网多断面联合状态估计方法。通过建立直角坐标系下基于二次型的配电网多断面联合状态估计模型,并采用正交变换法求解,实现对配电变压器变比的准确估计。IEEE 33节点修正系统及某实际配电网的算例分析结果表明,所提方法能够对配电变压器变比给出较为准确的估计,有助于及时发现并修正变比参数错误,减轻参数维护工作量,提升配电网状态估计精度。

埋地夹砂拱结构的受力特性影响分析

为研究埋地半椭圆形夹砂拱结构受力特性的影响规律,采用自制模型箱开展拱结构埋地特性的加载试验,测试其环向应变与竖向位移,建立埋地半椭圆形夹砂拱结构的ABAQUS数值计算模型并验证精度;采用有限元方法研究不同矢跨比、覆土高度和拱脚约束状态对拱结构受力和变形的影响规律。结果表明:0.30~0.45之间的四种矢跨比下,拱顶和拱脚位置是拱结构受力和变形的关键位置;覆土高度在60 cm、90 cm和120 cm三个高度变化时,增加覆土高度可以对拱结构起到较好的减载作用;拱脚由无约束向半约束和全约束状态转换时,拱结构受力的最不利位置由拱顶转移至拱脚,有利于结构整体受力。夹砂拱结构设计施工中,可将受力最不利位置作为安全控制点,且应关注拱结构的应力集中问题,同时采取减载等手段,以避免结构产生破坏。

数字金融、债务杠杆与企业全要素生产率

基于2011—2019年沪深A股上市公司数据,探讨数字金融对企业全要素生产率的内在联系及其影响机制。实证结果显示:数字金融对提升企业全要素生产率有着显著的促进作用,在考虑内生性问题和一系列稳健性检验之后,结论仍然成立;非国有企业、小规模企业以及处于东部和中部地区企业的全要素生产率受到数字金融发展的影响更为显著;数字金融发展提升企业全要素生产率的一个重要渠道是通过降低企业债务杠杆率来实现的。因此,在经济转型期间要引导数字金融成为企业发展新动力。

基于Kriging遗传算法的高速公路应急车道管控优化

针对如何在不同交通流状况下有效提高高速公路运行效率和降低安全风险的问题,提出基于Kriging代理模型的遗传算法优化应急车道管控策略。结合应急车道开放策略的时空特性设计数学优化模型,通过引入Kriging代理模型,结合遗传算法搭建优化框架,采用仿真软件获取数据训练代理模型,以此求解带有开放时间和开放空间双重约束的总行程时间与总碰撞暴露时间最小化问题。对车道控制时间与空间变量的变化频次进行了约束,并对目标函数中效率与安全指标权重变化对优化结果的影响进行了分析。实验表明:该优化方法使路网总行程时间减小14.9%,碰撞暴露时间减小44.2%,控制效果提升。