叉车转向桥的有限元分析

以YCC30D型内燃平衡重式叉车的横置油缸转向桥体为例,分析转向桥的受力情况,找到应力集中的部位,并运用ANSYS软件对叉车转向桥体进行模态分析与谱分析,得到转向桥体的固有频率及其在随机振动下的响应曲线,分析发生共振的可能性,验证了结构的强度,为进一步进行模型的优化提供了有力的数据.     

A finite element analysis of factors influencing total hip dislocation

A previously validated three-dimensional finite element model was used to study how several total hip component design and surgical placement variables contribute to resisting the propensity for posterior dislocation in the case of leg crossing in an erectly seated position. The computational formulation incorporated treatments of polyethylene material nonlinearity and large displacement sliding contact. The primary outcome measures were the peak intrinsic moment developed to resist dislocation, and the ranges of motion before neck on lip impingement and before frank dislocation. Modifications of the acetabular linear design (chamfer bevel angle, lip breadth, head center inset) involved trading off improved peak resisting moment for compromised range of motion and vice versa. Increases of head size led to substantial improvements in peak resisting moment, but if the head to neck diameter ratio was held constant, had almost no influence on the component range of motion. For the leg crossing event studied, increased component anteversion, and even more so increased tilt (less net abduction), achieved improvements in range of motion and in peak resisting moment, but these changes imply diminished resistance to anterior dislocation from extension and adduction motion inputs.     

Thermomechanical analysis of direct chill casting using finite element method

The transient nature of the start-up phase is the most critical phase in the direct chill (DC) casting during which the quality of the ingot is questioned. The hot crack and cold crack are the two major problems in the DC casting which originate during and after the solidification. In this work, the thermal, metallurgical, and the mechanical fields of DC casting are modeled. The attention is focused on the mushy state of alloy where the chances are high for the hot tearing. The heat conduction and metallurgical phase-change phenomenon are modeled together in a strongly coupled manner. An isothermal staggered approach is followed to couple the thermal and mechanical parts within a time step. Finite element method is used to discretize the thermal and mechanical field equations. A temperature-based fixed grid method is followed to incorporate the latent heat. The mushy state of alloy is characterized through the Norton-Hoff viscoplastic law and the solid phase is modeled through the Garafalo law. An axisymmetric round billet is simulated. The casting material is considered as AA1201 aluminum alloy. It is found that all the components of stress and viscoplastic strain are maximum at the billet center. Further, the start-up phase stresses and strains are always higher than the steady state phase. Therefore, the chances of hot crack formation are higher during the start-up phase and specifically at the billet center. It is proved that through the ramping procedure, the vulnerability of start-up phase can be lowered.     

Biomechanical aspects of the insect wing: an analysis using the finite element method

Insect wings appear as highly functional and largely optimized mechanical constructions. A series of stabilizing constructional elements have been 'designed' to cope with loading during flight. One such element is the expenditure of material in constructing the wing, i.e. the vein system of the wing and its arrangement. It functions like a zig-zag folding framework which stiffens the wing against aerodynamic bending moments. To quantify the quality of material distribution, models of a dragonfly wing and of a fly wing were calculated using the finite element method (FEM).     

Red cell distortion and conceptual basis of diffusing capacity estimates: finite element analysis

To understand the effects of dynamic shape distortion of red blood cells (RBCs) as it develops under high-flow conditions on the standard physiological and morphometric methods of estimating pulmonary diffusing capacity, we computed the uptake of CO across a two-dimensional geometric capillary model containing a variable number of equally spaced RBCs. RBCs are circular or parachute shaped, with the same perimeter length. Total CO diffusing capacity (DLCO) and membrane diffusing capacity (DMCO) were calculated by a finite element method. DLCO calculated at two levels of alveolar PO2 were used to estimate DMCO by the Roughton-Forster (RF) technique. The same capillary model was subjected to morphometric analysis by the random linear intercept method to obtain morphometric estimates of DMCO. Results show that shape distortion of RBCs significantly reduces capillary diffusive gas uptake. Shape distortion exaggerates the conceptual errors inherent in the RF technique (J. Appl. Physiol. 79: 1039-1047, 1995); errors are exaggerated at a high capillary hematocrit. Shape distortion also introduces additional error in morphometric estimates of DMCO caused by a biased sampling distribution of random linear intercepts; errors are exaggerated at a low capillary hematocrit.     

某空旷大跨度体育场馆的建模分析

针对体育场馆类空旷大跨度结构的设计特点,运用有限元程序,对某公司文化体育中心结构的整体受力性能、薄弱部位及大跨度网架屋盖对主体结构受力性能的影响与协同工作等问题进行了模拟分析.计算表明,此类结构具有扭转不规则性,薄弱部位常出现在空旷结构部位和弱连接部位;空旷框架部分存在相对变形大的现象.由于框架柱缺乏有效约束,其计算长度较大,P-△效应明显;网架屋盖在水平力及地震作用下对主体结构有不可忽视的作用,应考虑网架屋盖与下部框架结构的协同工作.实际设计中可考虑将网架部分按照一定的规则等代为钢梁,来近似考虑网架的刚度进行整体设计.     

宽厚板压力矫平压下模型理论建模与有限元分析

宽厚板压力矫平过程由于缺少精准可靠的压力矫平模型,工艺参数的设定主要依靠人工经验,制约了生产效率和产品质量的提升。针对实现全自动压力矫平关键瓶颈问题——压力矫平模型进行研究。采用弹塑性力学理论,结合压力矫平过程的特点,建立宽厚板压力矫平数学模型;在材料力学性能参数、初始平直度或曲率已知的情况下,自动计算出压平力、压头行程等参数;根据压力矫平模型计算出的数据,采用有限元方法模拟压力矫平过程,获得板材各节点位置和位移数据,计算出压力矫平后宽厚板的平直度。结果表明,各种工况下宽厚板的平直度小于2 mm/m,优于宽厚板的交货标准,证实了模型的可靠性。     

Elastoplastic finite element analysis of short-fiber-reinforced SiC/Al composites: effects of thermal treatment

Elastoplastic finite element analyses of realistic models of short-fiber-reinforced composites were extended to include the effects of prior thermal treatments on predictions of subsequent mechanical properties. Two three-dimensional models were used, one in which the fiber ends were transversely aligned and another in which they were staggered. Both models were found to be necessary for accurate predictions of the behavior of higher volume fraction composites. The temperature dependence of the yield stress of the matrix material was explicitly included in the analysis. The spatial and temporal history of calculated. The room temperature residual stresses were also predicted. Both the plastic deformation and the residual stresses in the matrix were spatially non-uniform and varied rapidly from the regions near the ends of the fiber to those near the midpoint. Predictions of subsequent tensile stress-strain properties were in good quantitative agreement with experiments. The presence of residual stresses and locally deformed regions caused the tensile behavior to differ from the compressive behavior. These differences were complex and depended on the volume fraction and aspect ratio of the reinforcement. The analyses provide detailed insight into the deformation mechanisms of these composites.     

Variation in labial shoulder geometry of metal ceramic crown preparations: a finite element analysis

BACKGROUND: The anatomic variation of the frontal sinus and frontal recess can create both a diagnostic and therapeutic challenge. Most cases of frontal sinus disease can now be treated by endoscopic approaches. For refractory cases or those with severe pathology, the microscopically controlled drainage (MCD) operation has at times been successful and spared the patient the morbidity of an external approach. The aim of this study was to evaluate microscopically controlled frontal sinus surgery in these difficult cases. MATERIAL AND METHODS: Prospective analysis was performed on the efficacy of MCD in patients for whom endoscopic sinus surgery had failed or in primary cases with severe pathology or unfavorable anatomy. The technique employs a self-retaining endonasal retractor and a diamond bur under microscopic visualization to remove solid bone (frontal spine) obstructing the sinus drainage and allow a wide opening of the frontal recess while causing minimal mucosal damage. Unilateral drainage (extended frontal sinus drainage operation), and in some cases bilateral drainage (median drainage procedure) is employed. RESULTS: With an average of 23 months of follow-up, over 90% of patients were either free of symptoms or substantially improved after the MCD procedure. Three patients required revision surgery (extend the opening into a median drainage procedure) for adequate relief of symptoms. CONCLUSIONS: The MCD procedure is highly successful in the treatment of frontal recess disease, particularly in those cases of severe pathology or difficult anatomy. It may be used in those cases refractory to standard endoscopic sinus surgery where an external approach and frontal sinus obliteration are contemplated. As with endoscopic sinus surgery, precise knowledge of the frontal recess and neighboring landmarks is critical, and adequate drainage with minimal mucosal disruption should be the goal.     

Cementless implant composition and femoral stress. A finite element analysis

Proximal atrophy and thigh pain are recognized problems with some cementless femoral stems in total hip arthroplasty. It is thought that reduced femoral stress from alterations in load transfer caused by an intramedullary stem contributes to proximal femoral atrophy. An increase in flexural rigidity and bone stress near the stem tip is thought to contribute to thigh pain. A three-dimensional finite element analysis study was performed to calculate stresses in the proximal femur and bone near the stem tip before and after implantation of a collared, proximally coated, cementless femoral prosthesis. The influence of prosthetic material was examined by changing implant composition from cobalt chrome to titanium alloy and leaving all other parameters constant. Femoral stress was increased twofold immediately below the collar with the titanium implant compared with the cobalt chrome. However, the proximal femoral stress in the titanium implanted model was still 1/10 that in the corresponding region of the unimplanted femur model. At the stem tip, as much as a 30% reduction in femoral stress was seen with the titanium stem compared with the cobalt chrome. These findings suggest biomechanical evidence of an advantage for titanium as an implant material compared with cobalt chrome for cementless femoral stems.     

铝电解槽三维热应力场非线性有限元分析

基于通用有限元软件ANSYS建立了某大型铝电解槽结构的三维实体模型和热应力场耦合分析的有限元模型.考虑材料非线性和接触非线性的基础上对电解槽结构强度进行了仿真计算,给出了槽壳和摇篮架的应力、应变云图,分析了电解槽结构的变形规律,并提出了结构优化的途径.以槽壳近似弹性体为目标,对不同组合载荷工况进行了反算,得出与实际更接近的荷载条件.     

基于有限元分析的动力设备状态分析及检修参数的优化

针对某大型动力设备振动问题,采用有限元工具建模、静力分析、模态分析,重点分析影响振动的关键因素对设备正常运行的影响,并调整关键因素的数值进行趋势分析。该方法的应用对于减小检修故障发生率、预知检修结果等具有重要意义。     

基于有限元法的拉伸弯曲矫直过程板形控制分析

 板形是带钢质量的重要判定指标,常见的板形缺陷有边浪、中浪、1/4浪等,其实质是残余应力在带宽上的分布不均。拉伸弯曲矫直机通过张力辊组、弯曲辊组和较真辊组的共同作用,使带钢在低于屈服强度的张力作用下发生塑性延伸,从而有效消除浪形缺陷,改善板形,提高带钢质量。然而在拉伸弯曲矫直机的设计和使用过程中,对拉伸弯曲矫直机参数的调整多基于经验,缺少理论指导。为了定量分析拉伸弯曲矫直机参数对浪形缺陷的改善效果,使拉伸弯曲矫直机在实际生产中发挥更好的作用,以某1 450 mm带钢酸洗冷轧生产线上的拉伸弯曲矫直机为研究对象,使用有限元软件ANSYS/LS-DYNA基于三维弹塑性有限元法建立了拉伸弯曲矫直机模型,对拉伸弯曲矫直机矫直过程进行了模拟,分析了张力和插入深度对初始浪形分别为边浪和中浪的带钢矫直后板形的影响规律。结果表明,经过拉伸弯曲矫直的带钢浪形缺陷得到显著改善;插入深度和张力对初始浪形缺陷分别为边浪和中浪的带钢板形的影响规律一致;3个辊组中矫直辊组的插入深度是影响带钢板形的主要因素,随着矫直辊组插入深度增大,带钢矫直后板形由边浪转变为平直,且随着矫直辊插入深度进一步增大,板形又由平直转变为边浪;随着入口张力增大,带钢矫直后板形由边浪转变为中浪。     

Thermomechanics of the cooling stage in casting processes: Three-dimensional finite element analysis and experimental validation

A thermomechanical three-dimensional (3-D) finite element analysis of solidification is presented. The heat transfer model is based on a multidomain analysis accounting for noncoincident meshes for the cast part and the different mold components. In each subdomain, a preconditioned conjugate gradient solver is used. The mechanical analysis assumes the mold is rigid. A thermoelastic-viscoplastic rheological model is used to compute the constrained shrinkage of the part, resulting in an effective local air gap width computation. At each time increment, a weak coupling of the heat transfer and mechanical analyses is performed. Comparisons of experimental measurements and model predictions are given in the case of a hollow cylindrical aluminum alloy part, showing a good quantitative agreement. An application to an industrial aluminum casting is presented, illustrating the practical interest of thermomechanical computations in solidification analysis.     

高强钢筋热压缩过程的本构分析及有限元模拟

为了研究Nb/V微合金化钢筋的热变形行为,采用Gleeble-3500热模拟机对Nb和Nb/V微合金化的20MnSi钢进行单轴热压缩试验.通过对其不同形变条件(变形温度和应变速率)下的真应力-应变曲线进行分析,建立可以表征20MnSiNb和20MnSiNbV钢应力、应变、应变速率和温度四者关系的本构方程,并将该本构方程...     

高速公路深路堑边坡应力及位移的有限元分析

为了研究山区高速公路深路堑边坡的稳定性问题,基于三维非线性应力及位移有限元计算,对边坡稳定性进行了数值分析,并与Sarma法的计算结果进行了对比.结果表明,有限元法解决边坡问题可以起到其他方法不可替代的重要作用.     

电渣重熔过程中焦耳热与温度场的有限元分析

建立了电渣重熔过程中的电磁场与温度场的耦合数学模型,利用商业软件ANSYS对包括电极、渣池和钢锭的一体化电渣重熔系统电磁场、焦耳热场和温度场进行有限元计算,并分析冷却水温对重熔系统温度的影响.结果表明:重熔系统中的焦耳热主要分布在渣池中,其最大值出现在渣池与电极端口接触处,即电流密度最大处;重熔系统的最高温度出现在电极...     

热轧机有限元与神经网络集成建模

以某钢厂1580热连轧生产数据为基础,提出一种有限元与神经网络集成建模的方法.该方法首先对轧制过程的塑性变形进行有限元建模,然后结合有限元数值分析方法和智能技术的优点,实现有限元和神经网络的集成建模.集成模型中的神经网络模型为有限元模型提供参数调整的依据,并且在神经网络训练过程中使用改进的混沌粒子群优化算法对神经网络进行优化.通过与现场实际生产数据进行比较,验证了该模型的有效性.