基于等效有限元方法的液压挖掘机工作装置动力学及特性研究

根据液压挖掘机工作装置机械臂运动和受力特点,对其进行动力学分析。采用基于集中质量和惯量的等效有限元法建立液压挖掘机机械臂的动力学微分方程,运用龙格-库塔(Runge-Kutta)数值求解法对运动微分方程进行推导和数值求解,对各臂杆的动力学特性进行了分析。采用动力学仿真软件ADAMS建立了液压挖掘机工作装置的虚拟样机模型,选取与数值求解相同工况的参数进行仿真分析。通过对比仿真结果和数值求解两种方法得到的动力学特性曲线,结果基本一致,表明机械臂动力学建模方法的正确性。

PC斜拉式桁架梁桥动力特性

基于有限元理论,以某PC斜拉式桁架梁桥为工程实例,采用等效有限元法,建立三维有限元模型,对该结构进行动力计算分析。研究了桥墩刚度、横系梁刚度、桁架片刚度、桥墩高度、桥面宽度等参数对结构动力特性的影响,通过对结构的自振振型及频率进行相应分析,得出结构参数变化对结构的横向刚度、竖向刚度、纵向刚度和扭转刚度及其他动力特性的影响程度及规律。结果表明:桥墩的高度及刚度很大程度上决定了结构的纵向刚度,而横系梁的刚度是影响结构的横向刚度及抗扭刚度的主要因素。

FEM modeling of softened base metal in narrow-gap joint by CMT+P MIX welding procedure

A required finite element method（FEM） model applicable for narrow gap CMT and CMT＋P MIX welding was established based on the interactions between arc,base metal and filler metal.A novel method of simplifying wire feeding pulses and heat input pulses was supposed under the conduction of equivalent input.The method together with composed double-ellipse heat sources was included in the model.The model was employed in the investigation of thermal cycling and the identification of the softened zone of AA7A52 base plates.Low-frequency behavior emerged in the form of low-cooling rate sects,which were not expected under experimental conditions.The softened zone including the quenched zone and averaging zone of the base plate was much wider internal the base plate than that close to the surfaces.The reliability of the predictions in thermal cycling was supported by infrared imaging test results of the thermal cycle process.

Calculation of effective temperature for pavement rutting using numerical simulation methods

In order to predict the long-term rutting of asphalt pavement, the effective temperature for pavement rutting is calculated using the numerical simulation method. The transient temperature field of asphalt pavement was simulated based on actual meteorological data of Nanjing. 24-hour rutting development under a transient temperature field was calculated in each month. The rutting depth accumulated under the static temperature field was also estimated and the relationship between constant temperature parameters was analyzed. Then the effective temperature for pavement rutting was determined based on the rutting equivalence principle. The results show that the monthly effective temperature is above 40 t in July and August, while in June and September it ranges from 30 to 40 Rutting development can be ignored when the monthly effective temperature is less than 30 t. The yearly effective temperature for rutting in Nanjing is around 38. 5 t. The long-term rutting prediction model based on the effective temperature can reflect the influences of meteorological factors and traffic time distribution.

EVALUATION OF ELECTROMAGNETIC SCATTERING OF TWO DIMENSIONAL CONDUCTING OBJECTS--TE CASE

A hybrid technique is developed for the evaluation of two dimensional electromagnetic scattering from electrically large conducting bodies with cracks on their surfaces (TE case). The edge based finite element method (FEM) is employed to compute the scattering from the cracks. Physical optics (PO) and physical theory of diffraction (PTD) are utilized to evaluate the scattering from the large bodies with the cracks filled with perfect conductors. These two methods are combined by an efficient coupling scheme. Some of numerical results are presented. It is shown that the hybrid technique has some advantages over other methods in regard to saving computer memory units and CPU time.

绕组周向分布圆筒型初级永磁直线电机结构及静态特性分析

提出一种绕组周向分布圆筒型初级永磁直线电机(tubular primary permanent magnet linear machine,TPPMLM)。与传统圆筒型初级永磁直线电机相比,该电机采用集中式绕组,每相绕组周向分布,初级铁心齿部及轭部由矽钢片一次叠压而成,初级制造工艺简单。同时,永磁体位于初级,次级仅由导磁铁心组成,可降低长距离驱动系统成本。该文阐述该电机的结构特点,给出工作原理,并分别利用磁路法及等效二维有限元法建立单元电机等效磁路模型及仿真模型,对静态特性分析,包括磁场、反电动势、定位力及电磁推力等。三维有限元模型及样机实验结果分别验证等效二维有限元模型的有效性及拓扑结构设计方法的正确性,同时,反电动势测试结果表明该拓扑不存在纵向端部效应导致的各相反电动势不对称问题。

Influence of longitudinal slope on the mechanical response of steel deck pavement

In order to study the influence of longitudinal slope on the mechanical response of steel deck pavement,a method of slope-modulus transformation was proposed for the mechanical analysis of the steel deck pavement based on the time-temperature equivalence principle.Considering the mechanical action on a slope,a finite element model of the deck pavement was established to determine the critical load position of tensileand shear stress of the steel deck pavement.Additionally,the influence of longitudinal slope on the mechanical response of the deck pavement under the conditions of uniform speed and emergency braking was analyzed.The results indicate that the maximum transverse tensile stress at the pavement surface and the maximum transverse shear stress at the pavement bottom are always greater than their longitudinal counterparts under uniform speed.Under emergency braking,however,the critical slope gradient of t e maximum transverse and longitudinal tensile stress at t e pavement surface is 6%.The maximum longitudinal shear stess at t e pavement bottom is always greater ta n t e maximum tansverse shear stess.This stidy is helpful in t e strctural design of large longitudinal slope steel deck pavements.

通道宽度比对侧向挤压坯料变形的影响

采用刚塑性有限元研究了不同通道宽度比侧向挤压时材料的变形分布、载荷及速度场。结果表明,随通道宽度比的增加,等效应变较大的区域逐渐由坯料的上部转到下部。宽度比为2时,通道拐角外侧坯料存在少量变形死区,使坯料下部变形严重。随通道宽度比的降低,坯料中变形较均匀的区域减小,拐角处间隙增大。当宽度比为0.67时,坯料产生明显畸变。挤压过程中的最大载荷随通道宽度比增加而增加。