高速列车荷载下桩网结构路基竖向动应力传递分析

依托哈尔滨—大连高速铁路典型断面建立桩网结构路基有限元模型,分析路基高度和桩间距对列车荷载作用下路基竖向动应力传递的影响。研究结果表明:竖向动应力沿路堤深度逐渐减小,距桩顶同一距离的水平面上桩顶处竖向动应力最大,四桩形心处竖向动应力最小;路堤高度较小时土拱效应较弱,桩顶应力集中效应起主导作用;随着桩间距的增大土拱高度增加,竖向应力提前由衰减变为增加且单个土拱拱脚所需承担的竖向动荷载增加;计算得到的竖向动应力衰减系数在中国规范与日本规范计算结果之间。

Forced Axial and Torsional Vibrations of a Shaft Line Using the Transfer Matrix Method Related to Solution Coefficients

This present paper deals with a mathematical description of linear axial and torsional vibrations. The normal and tangential stress tensor components produced by axial-torsional deformations and vibrations in the propeller and intermediate shafts, under the influence of propeller-induced static and variable hydrodynamic excitations are also studied. The transfer matrix method related to the constant coefficients of differential equation solutions is used. The advantage of the latter as compared with a well-known method of transfer matrix associated with state vector is the possibility of reducing the number of multiplied matrices when adjacent shaft segments have the same material properties and diameters. The results show that there is no risk of buckling and confirm that the strength of the shaft line depends on the value of the static tangential stresses which is the most important component of the stress tensor.

Application of artificial intelligent systems for real power transfer allocation

The application of various artificial intelligent(AI) techniques,namely artificial neural network(ANN),adaptive neuro fuzzy interface system(ANFIS),genetic algorithm optimized least square support vector machine(GA-LSSVM) and multivariable regression(MVR) models was presented to identify the real power transfer between generators and loads.These AI techniques adopt supervised learning,which first uses modified nodal equation(MNE) method to determine real power contribution from each generator to loads.Then the results of MNE method and load flow information are utilized to estimate the power transfer using AI techniques.The 25-bus equivalent system of south Malaysia is utilized as a test system to illustrate the effectiveness of various AI methods compared to that of the MNE method.

Influence of excavation beneath existing building on dynamic impedances of underpinning pile considering stress history

The addition of basement beneath existing building changes the underpinning pile from fully embedded to partially embedded,and thus influences the mechanical properties of pile.In the past,scholars paid attention to the change in the bearing capacity of pile but neglected the difference of dynamic characteristics before and after construction,and potential changes in stress history of remaining soil are also ignored.In this work,a calculation model is built to investigate the influence of excavation on dynamic impedance of underpinning pile considering the effect of stress history.The soil is simulated by the dynamic Winkler foundation,which is characterized by springs and dashpots.Properties of remaining soil after excavation are updated to consider the effect of stress history through modifying the initial shear modulus and related parameters.The dynamic impedance of pile after excavation is obtained based on the transfer matrix method.The parameter study is carried out to evaluate the dynamic impedance with various excavation depths,considering or ignoring stress history effect,and various element lengths.The results show that shallow soil plays an important role to dynamic impedance,and overestimated dynamic impedance is obtained if not considering the stress history effect.

Stress transfer around a broken fiber in unidirectional fiber-reinforced composites considering matrix damage evolution and interface slipping

A shear-lag model is applied to study the stress transfer around a broken fiber within unidirectional fiber-reinforced composites(FRC) subjected to uniaxial tensile loading along the fiber direction.The matrix damage and interfacial debonding,which are the main failure modes,are considered in the model.The maximum stress criterion with the linear damage evolution theory is used for the matrix.The slipping friction stress is considered in the interfacial debonding region using Coulomb friction theory,in which interfacial clamping stress comes from radial residual stress and mismatch of Poisson's ratios of constituents(fiber and matrix).The stress distributions in the fiber and matrix are obtained by the shear-lag theory added with boundary conditions,which includes force continuity and displacement compatibility constraints in the broken and neighboring intact fibers.The result gives axial stress distribution in fibers and shear stress in the interface and compares the theory reasonably well with the measurement by a polarized light microscope.The relation curves between damage,debonding and ineffective region lengths with external strain loading are obtained.

COMPUTATION OF MOMENTUM TRANSFER COEFFICIENT AND CONVEYANCE CAPACITY IN COMPOUND CHANNELS

The momentum transfer coefficient is an important parameter for determining the apparent shear stress at the vertical interface between the main channel and its associated flood plains,the cross-sectional mean velocity and the discharge capacity in compound channels. In this article,under the Boussinesq assumption and through analyzing the characteristics of velocity distribution in the interacting region between the main channel and its associated flood plain,the expression of momentum transfer coefficient was theoretically derived. On the basis of force balance,the expression of vertical apparent shear stress was obtained. By applying the experimental data from the British Engineering Research Council Flood Channel Facility (SERC-FCF),the relationship between the momentum transfer coefficient with the relative depth and the ratio of the flood plain width to the main channel width,was established,And hence the conveyance capacity in compound channels was calculated with Liu and Dong’s method. The computed results show that the momentum transfer coefficient relationship obtained is viable.