表面形态抗冲蚀三维数值模拟

利用有限元软件ANSYS／LS—DYNA,对光滑试件和凸包形、凹槽形表面形态的45号钢试件的耐冲蚀性能,进行了三维数值模拟,计算冲蚀磨损过程中等效应力的变化情况。结果表明,试件数值模拟的冲蚀情况与试验吻合良好。这说明选用适当的ANSYS／LS—DYNA单元类型和设置合理的参数,完全可以实现对光滑试件和两种不同的表面形态试件的耐冲蚀性能的数值模拟,本文对于研究表面形态耐冲蚀机理和进行冲蚀磨损预报有一定的借鉴意义。     

Analysis on Reinforced Concrete Flexural Members Using Deformation Condensation Method

Traditional nonlinear analysis of RC structures usually adopts nonlinear FEM based on continuum mechanics, and it is hard to reflect macroscopic deformation characteristic, such as local rotation in crack sections and plastic hinge of failure stage. From the perspective of physical model, a new deformation condensation method is developed. The analysis of RC flexural members in the 1-D elastic problem involve three stages based on the concept of deformation condensation. RC flexural members were divided into several elements according to average crack spacing to get numerical model consistent with the physical model with higher computational efficiency tests of RC flexural members reinforced with high strength rebars conducted by Institute of Prestressed Structures in Tongji University, were simulated and the simulation results agreed well with the experimental data indicating that this novel method is applicable.     

湖羊生长发育曲线模型预测及趋势分析

本试验旨在研究湖羊的生长发育状况,初步探讨湖羊的生长发育曲线模型并作出趋势分析,并根据此模型建立的生长曲线为湖羊的选育和改善饲养管理提供依据,从而找出湖羊养殖的最佳生长点和上市点.选用木板高床饲养的湖羊31只,测定了初生重、7日龄、14日龄、1～12月龄的体重.采用Logistic、Gompertz和Von Bertalanffy 3种生长曲线模型对湖羊的生长曲线进行拟合.结果发现,Logistic和Gompertz模型对湖羊生长发育的拟合效果较好,其值均高于0.97,其中以Gompertz为最优.利用最优拟合模型进一步分析模型拟合参数,湖羊在2月龄时出现生长拐点.     

番鸭体重生长非线性混合效应模型评价的研究

【目的】定量描述和估计本地番鸭体重生长的轨迹和参数。【方法】本研究对116只番鸭进行了21 weeks的饲养和观测;利用5种生长函数(Gompertz、Logistic、Von Bertalanffy、Richards和Brody)拟合了番鸭体重生长的非线性混合效应模型;分别计算了这些模型的8个生长参数(成熟体重、拐点日龄、拐点体重、初生体重、绝对生长率、相对生长率、绝对成熟率和相对成熟率);根据信息准则、误差方差的大小和生长参数估计值的准确度,比较了不同模型间的拟合和估计结果。【结果】与非线性固定效应模型比较,5种非线性混合效应模型拟合的番鸭体重生长方程和估计的8个生长参数,其准确度整体上提高了许多;全群番鸭体重生长Gompertz非线性混合效应模型,其信息准则最小,误差方差减少量达99.92%;雄、雌番鸭体重生长Richards非线性混合效应模型, 其信息准则最小,误差方差减少量分别是89.80%、91.81%。【结论】Gompertz和Richards非线性混合效应模型分别是评价全群和雄、雌番鸭体重生长的最优模型。     

Multiplex analytical method for metal three dimensional flow of heavy rail rolling by universal mill

With the monitoring data of groundwater level of some reservoir slope, the nonlinear combined model was established on the basis of establishing the time series method and speed analysis method. Upon the comparison, it was found that the precision of non linear combined model was higher than that of single model. It was an effective prediction method for groundwater level of reservoir slope and could be employed for stability prediction of reservoir slope.     

Stability Behavior of Shuttle-Shaped Steel Lattice Columns With Bending Moment

The stability behavior of shuttle-shaped steel lattice columns subject to combined axial force and bending moment was examined through elastic buckling analysis and geometrically and materially nonlinear analysis. Firstly, the concept of section stiffness variation ratio is proposed for shuttle-shaped lattice columns and the elastic buckling behavior is discussed. Then, the effect of bending moment on the stability behavior of lattice columns is investigated, with the emphasis on the development of axial stress, bending stress and shear stress. The influence of column component spacing and diaphragm thickness on the stability bearing capacity is also analyzed. It is shown that the elastic buckling mode of the lattice column is dependent on its section stiffness variation ratio; for lattice columns with C-shaped buckling mode, the reduction in stability bearing capacity caused by bending moment is smaller than that of columns with S-shaped buckling mode; the maximum stability bearing capacity of the lattice column can be achieved by adjusting the column component spacing, and the spacing corresponding to the maximum capacity is basically consistent with the critical spacing for transformation of C-shaped buckling mode and S-shaped mode; and it is more effective to increase the thickness of columns with S-shaped buckling mode to get larger bearing capacity.     

Analysis of ultimate load and mechanismsof failure in large cast steel joints

Based on a project of pipe truss roof framing in Chengdu, the ultimate limit state analysis is performed on cast steel joints by using FEM, in which Linear hardening elastic-plastic constitutive model is considered. The results show that, the joint has a great accumulation of plastic strain in ultimate loads, and the point of maximum stress is different from that in elastic with the development of the yielding zone. The paper propoes to use rate-type tensor for the large strain geometric nonlinear problem, shows the criterion of failure formation , and indicates that its essential to apply limit state analysis to the determination of the weakest location on cast steel joint design, which provides basis for understanding the failure modes and failure mechanism of cast steel joint and the cast steel joint design.     

红松树高-胸径的非线性混合效应模型研究

以吉林省汪清林业局的蒙古栎阔叶混交林和云冷杉阔叶混交林24块固定样地中的2598株红松为研究对象,利用Chapman-Richards方程建立了不含随机效应与含随机效应的单木树高-胸径简单模型和广义模型。模型拟合和检验的评价指标主要包括调整决定系数(R2a)、平均相对误差绝对值(RMA)和均方根误差(RMSE)。对于混合效应模型,设计了随机抽取、抽胸径最大的树、抽胸径最小的树和抽平均木4种抽样方案计算随机参数,通过对比4种抽样设计下模型的误差统计量,分析了不同抽样设计下样本数量和预测精度的关系。结果表明:基于混合效应模型的红松单木树高-胸径模型拟合效果(简单模型的R2a在0.753~0.886之间,RMA在11.3%~15.1%之间,RMSE在1.38~2.01m之间;广义模型的R2a在0.754~0.886之间,RMA在11.1%~15.0%之间,RMSE在1.38~2.01m之间)优于不含随机参数的红松单木树高-胸径模型(简单模型的R2a在0.502~0.868之间,RMA在12.2%~17.8%之间,RMSE在1.42~2.65m之间;广义模型的R2a在0.711~0.877之间,RMA在11.6%~17.2%之间,RMSE在1.41~2.10m之间);包含随机效应的简单模型和广义模型拟合效果没有明显的差异,表明基于混合效应模型的单木树高-胸径简单模型可以很好地描述树高-胸径关系在不同森林类型、不同样地间的差异,因此不需要在树高-胸径模型中增加其他自变量;抽取平均木的抽样设计优于其他3种抽样设计,且抽取4株平均木时,预测精度提升最为明显,综合预测精度和调查成本的考虑,在实践中应用包含随机效应的红松树高-胸径模型时,推荐在样地中抽取4株平均木测量其树高来估计随机参数。      

基于神经网络模型的空燃比非线性模型预测控制

采用基于径向基神经网络（RBFNN）模型的非线性模型预测控制方法,被控对象选择火花塞点火（SI）发动机的空燃比（AFR）高度非线性复杂系统,利用渐消记忆最小二乘法实现基于RBFNN的SI发动机AFR系统建模以及参数在线自适应更新。针对非线性模型预测控制中寻优问题,运用序列二次规划滤子算法对最优控制序列进行求解,并加入滤子技术避免了罚函数的使用。在相同的实验环境下,与PI控制算法和Volterra模型预测控制方法进行仿真对比实验,结果表明,所提算法的控制效果明显优于其他两种方法。     

一类四阶非线性微分方程边值问题正解的存在性

研究一类特殊形式的四阶非线性常微分方程边值问题,给出其正解存在的充分条件,并利用锥压缩与锥拉伸不动点定理证明正解的存在性。