某钢结构栈桥变形异常问题分析

针对某既有工业类钢结构栈桥项目的变形,根据现场观察、调查了解、现场检测、结构体系分析,推测出产生该变形的原因后,在不增加额外荷载和约束的前提下,通过计算模型的分步施工来实现对现状变形的拟合,进而可以对构件的承载力、整体结构的安全性作出更真实有效的分析,该方法对于既有建筑的变形分析是一种比较实用的方法。

主动主反射面天线促动器调整量计算与误差分析

主动主反射面天线通过调整安装在面板下方的促动器来提高表面精度,现有的促动器调整量计算方法多数忽略了面板弹性变形对调整精度的影响。文中通过力学仿真模拟来表征促动器调整过程对面板自身弹性变形的影响。首先,构建单块反射面面板变形拟合模型,并对拟合模型的权重进行优化,进而推导出整个反射面的变形拟合模型;其次,考虑到实际工程中相邻面板共用促动器,因此对促动器编号进行归并,进而推导出相邻面板共用促动器时促动器最佳调整量的计算模型。为了验证面板变形拟合模型的计算精度,分别从拟合模型的变形表征能力和促动器调整量的计算精度两个方面开展仿真验证工作,并从促动器调整误差和促动器故障两个方面分析促动器调整误差对反射面调整精度的影响,为工程中评估促动器调整精度提供参考。

基于国密技术的地理信息数据安全应用方法初探

随着智慧城市建设的推进与城市精准管理需求的不断提升,各部门的精准化、智能化的高效管理需求对地理信息数据提出了越来越高的要求。然而,当前地理信息服务模式在以下方面存在不足:一是部门需要更快速高效的地理信息数据更新服务;二是各部门精准管理需求越来越高,而当前空间位置精度(非线性脱敏处理后)无法满足应用需求。因此,通过本文的研究,是期望通过解决敏感数据的授权使用问题和安全保障,从而推动地理信息数据获取处理全面提速,提高综合服务能力。

Computer aided stitching approach for dental restoration models

According to the bio-characteristics of the lower and upper cavity surfaces of dental restoration, a stitching approach is proposed based on a virtual zipper working mechanism and a minimization of the surface total curvature energy, which is used to resolve the stitching problems existing during computer-aided design for dental restorations. First, the two boundaries corresponding to the lower and upper surfaces are triangulated based on the zipper working mechanism to generate the initial stitching surface patch, of which the edges are distributed uniformly between the boundaries. Secondly, the initial stitching surface patch is subdivided and deformed to reconstruct an optimized surface patch according to the bio-characteristics of the teeth. The optimized surface patch is minimally distinguishable from the surrounding mesh in smoothness and density, and it can stitch the upper and lower cavity surfaces naturally. The experimental results show that the dental restorations obtained by the proposed method can satisfy both the shape aesthetic and the fitting accuracy, and meet the requirements of clinical oral medicine.

A method for prediction of unstable deformation in hot forging process by simulation

A method is proposed for prediction of the unstable deformation in hot forging process using both the determined thermomechnical parameter windows of the unstable deformation zones and finite element simulation. Taking Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy as the testing material, the thermomechnical parameter windows of the unstable deformation zones for the Ti-alloy are integrated into a commercial finite element simulation software platform. The distribution and variation of the unstable deformation zones of the alloy in hot compression process are simulated and predicted using the tailor-made finite element codes in the finite element platform. The simulation results tally with the physical experiments and the proposed method for simulation and prediction of the unstable deformation is thus verified and its efficiency is validated.

Simulation and experiment analysis on thermal deformation of tool system in single-point diamond turning of aluminum alloy

The aim of this work is to simulate thermal deformation of tool system and investigate the influence of cutting parameters on it in single-point diamond turning(SPDT) of aluminum alloy. The experiments with various cutting parameters were conducted. Cutting temperature was measured by FLIR A315 infrared thermal imager. Tool wear was measured by scanning electron microscope(SEM). The numerical model of heat flux considering tool wear generated in cutting zone was established. Then two-step finite element method(FEM) simulations matching the experimental conditions were carried out to simulate the thermal deformation. In addition, the tests of deformation of tool system were performed to verify previous simulation results. And then the influence of cutting parameters on thermal deformation was investigated. The results show that the temperature and thermal deformation from simulations agree well with the results from experiments in the same conditions. The maximum thermal deformation of tool reaches to 7 μm. The average flank wear width and cutting speed are the dominant factors affecting thermal deformation, and the effective way to decrease the thermal deformation of tool is to control the tool wear and the cutting speed.

Physical simulation of hot deformation of TiAl based alloy

In order to establish a model between the grain size and the process parameters, the hot deformation behaviors of Ti 49.5Al alloy was investigated by isothermal compressive tests at temperatures ranging from 800 to 1?100 ℃ with strain rates of 10 -3 10 -1 s -1 . Within this range, the deformation behavior obeys the power law relationship, which can be described using the kinetic rate equation. The stress exponent, n , has a value of about 5.0, and the apparent activation energy is about 320 J/mol, which fits well with the value estimated in previous investigations. The results show that, the dependence of flow stress on the recrystallized grain size can be expressed by the equation: σ=K 1d rex -0 56 . The relationship between the deformed microstructure and the process control parameter can be expressed by the formula: lg d rex =-0 281?1gZ +3 908?1.

Molecular dynamics simulation on plasticity deformation mechanism and failure near void for magnesium alloy

The plastic deformation processes of magnesium alloys near a void at atomic scale level were examined through molecular dynamics(MD)simulation.The modified embedded atom method(MEAM)potentials were employed to characterize the interaction between atoms of the magnesium alloy specimen with only a void.The void growth and crystal failure processes for hexagonal close-packed(hcp)structure were observed.The calculating results reveal that the deformation mechanism near a void in magnesium alloy is a complex process.The passivation around the void,dislocation emission,and coalescence of the void and micro-cavities lead to rapid void growth.

Simulation of coupled THM process in surrounding rock mass of nuclear waste repository in argillaceous formation

To investigate and analyze the thermo-hydro-mechanical(THM) coupling phenomena of a surrounding rock mass in an argillaceous formation, a nuclear waste disposal concept in drifts was represented physically in an in-situ test way. A transversely isotropic model was employed to reproduce the whole test process numerically. Parameters of the rock mass were determined by laboratory and in-situ experiments. Based on the numerical simulation results and in-situ test data, the variation processes of pore water pressure, temperature and deformation of surrounding rock were analyzed. Both the measured data and numerical results reveal that the thermal perturbation is the principal driving force which leads to the variation of pore water pressure and deformations in the surrounding rock. The temperature, pore pressure and deformation of rock mass change rapidly at each initial heating stage with a constant heating power. The temperature field near the heater borehole is relatively steady in the subsequent stages of the heating phase. However, the pore pressure and deformation fields decrease gradually with temperature remaining unchanged condition. It also shows that a transversely isotropic model can reproduce the THM coupling effects generating in the near-field of a nuclear waste repository in an argillaceous formation.

Deformation simulation of low-temperature high-speed extrusion for 6063 Al alloy

The hot compression test of 6063 Al alloy was performed on a Gleeble-1500 thermo-simulation machine, and the forming of 6063 rod cxtrudate in low-temperature high-speed extrusion was simulated with extrusion ratio of 25 on the platform of DEFORM 2D successfully. From the compression experimental results, the flow stress model of this Al alloy is obtained which could be the constitutive equation in the simulation of low-temperature high-speed extrusion process. From the numerical simulation results, there is a higher strain concentration at the entrance of the die and the exit temperature reaches up to 522 ℃ in low-temperature high-speed extrusion, which approaches to the quenching temperature of the 6063 Al alloy. The results show that the low-temperature high-speed extrusion method as a promsing one can reduce energy consumption effectively.

Simulation of texture evolution and deformation mechanism in Mg-3Al-1Zn alloy during uniaxial compression

The effects of starting texture on he flow curves, and microstructure and texture evolutions of AZ31(Mg-3Al-1Zn-0.3Mn in wt.%) alloy during uniaxial compression at room temperature have been investigated by experiments and simulations. Two kinds of cylindrical compression samples were cut from the AZ31 extruded rod: one was cut with the compression direction parallel to the extruded direction(ED), and the other was cut with the compression axis perpendicular to the ED. The samples were termed as C//ED sample and C⊥ED sample, respectively. The results indicate that the general characteristics of flow curves and texture evolutions in both C⊥ED and C//ED samples during compression can be well explained by the relative activities of deformation mechanisms, which show a strong orientation dependence on the initial textures and the current texture. A significant yield behavior can be induced by {10-12} twinning at the starting deformation, and the lower yield stress in C⊥ED sample can be enhanced by the high activity of basal slip. The work hardening behavior is related to the activities of basal slip, pyramidal <c+a> slip, {10-12} twinning, as well as {10-11} twinning. However, the activity of prismatic slip is insensitive to the starting texture, and mostly negligible in all samples.

Deformation dependence of symmetry energy coefficients of nuclei

Based on the semi-classical Thomas-Fermi approximation together with the Skyrme energy-density functional, we study the deformation dependence of symmetry energy coefficients of finite nuclei. The symmetry energy coefficients of nuclei with mass number A = 40, 100, 150, 208 are extracted from two-parameter parabola fitting to the calculated energy per particle. We find that the symmetry energy coefficients decrease with the increase of nuclear quadrupole deformations, which is mainly due to the isospin dependence of the difference between the proton and neutron surface diffuseness. Large deformations of nuclei can cause the change of the symmetry energy coefficient by about 0.5 Me V and the influence of nuclear deformations on the symmetry energy coefficients is more evident for light and intermediate nuclei.