基于梯度塑性理论的动力软化问题分析

对于动力应变软化问题 ,采用梯度塑性模型进行分析 ,该模型能够有效地克服软化材料在有限元分析中的网格依赖性问题。对于动力非线性软化方程的求解则利用基于参变量变分原理的参数二次规划方法。对于结构动力方程时域上的求解则采用传统的 Newm ark方法。本文的算法与传统方法相比在求解基于梯度塑性模型的非线性动力软化问题时保持了已有参数二次规划算法的优良特性 ,有实现简单与稳定性好等优点。给出的数值算例证实了本文的理论工作与所研制程序的正确性。

基床式基础防波堤的动力软化判别标准的研究

以长江口深水航道治理二期工程为依托,进行基床基础防波堤的动力软化判别标准的研究,分析在波浪作用下3个不同沉降量的典型断面下卧地基土的自重应力、附加静应力、波浪作用的附加动应力分布间的关系,初步得出该地区软粘土可能出现动力软化现象的判别标准。

精密高速电主轴动力学特性及轴承刚度软化分析

针对某精密高速电主轴系统,介绍主轴的系统结构,分析其高速加工状态下的特点和影响要素,对主轴和轴承采用有限元建模方法,用弹簧阻尼单元模拟主轴轴承支承。对不同弹簧单元布置形式下主轴系统的静力学特性,谐响应和模态进行了分析研究。在主轴高速加工的状态下,采用有限元法研究了基于高速旋转状态下轴承软化效应的主轴系统动特性,结果表明该种方法对于高速运行状态下能一定程度对动力学特性的变化规律进行仿真模拟,为快速分析高速下由于轴承软化现象引起的系统固有频率变化提供了一种思路。

一种热轧双相钢在γ和γ+α相区的静态软化动力学研究

对含 0 .1 9%碳的热轧双相钢分别在γ和γ +α相区进行双道次压缩试验 ,研究在不同变形温度和变形速率下钢的静态软化比随着间隙时间的变化规律。结果表明 ,在γ相区 ,随着变形温度的升高、变形速率的增加和间隙时间的延长 ,钢的静态软化比增加。在一定条件下 ,静态软化比可以达到 1 0 0 %。根据研究结果 ,对γ相区的静态再结晶动力学进行模型化。在γ +α相区 ,钢的静态软化比较低 ,它不仅受到变形温度、变形速率和间隙时间的影响 ,还受到两相组织组份的影响。

计入柔性梁动力刚化/软化效应的一种新方法

提出柔性梁的动力刚化/软化效应的本质是柔性梁的大范围运动所导致的梁内轴向力对于梁的横向弹性振动所产生的影响效应。给出了柔性梁动力学建模中计入动力刚化/软化效应的一种新方法:通过考虑大范围运动所导致的梁内轴向力对于梁的横向弹性振动所产生的影响,来达到动力学建模中计入柔性梁动力刚化/软化效应的目的。这种方法同目前已有的计入柔性梁动力刚化/软化效应的方法相比,具有直观、简单、物理概念清晰和符号运算简便的优点。通过对一旋转柔性梁的横向弹性振动的动力学建模和计算为例,具体演示了如何应用本文的方法计入柔性梁的动力刚化效应,同时也说明了本文方法在应用实施上的便捷性。最后,将本文的计算结果同相关文献的对应结果相比较,验证了本文方法的正确性。

深部洞室开挖卸荷分区破裂机制的动力分析

随着地下工程开挖深度的增加,深部岩体将处于高应力和复杂的地质环境中,产生与浅埋洞室破坏模式迥异的分区破裂现象。深部洞室在动力卸荷作用下,基于应变梯度理论和损伤软化模型,建立了弹塑性损伤软化动力模型,推导了含有应变梯度项的运动方程、平衡方程和边界条件,提出相应的破坏判据,采用Runge-Kutta方法和Matlab数值软件求得不同卸载时刻围岩附加位移场、应力场和开挖后围岩总位移场、应力场,得到深部洞室围岩分区破裂的动态形成过程和发展规律。由理论计算值与地质力学模型试验实测值对比分析得知,围岩的径向位移、径向应力和切向应力出现波峰和波谷交替振荡的变化规律,理论计算得到的破裂区和非破裂区的宽度和数量与试验实测值有很好的一致性,证实了该模型分析分区破裂现象的适用性,对以后深部地下工程围岩变形破坏和支护设计提供理论支持。

大范围运动刚体上矩形薄板力学行为分析

采用Hamilton变分原理建立了大范围运动平板的动力学模型.从理论上证明了不同大范围运动状态下平板中既可存在动力刚化效应,也可存在动力软化效应,且动力软化效应还可使板的平衡状态发生分岔而失稳.采用假设模态法验证了理论分析结果并得到了分岔临界值和近似后屈曲解.

半圆型海堤断面的结构设计

简要介绍了半圆型海堤结构断面设计全过程,包括断面主体构件的强度分析,断面各组成部分的尺度确定原则,改善地基承载力的若干项措施等。并对软基上半圆型海堤结构断面设计的一些特点和应注意的问题做了说明。

轴对称匀速转动状态下矩形薄板的动态特性与屈曲分析

应用Hamilton原理建立了轴对称匀速转动状态下对边简支对边自由矩形薄板的非线性动力学方程,采用假设模态法解析分析了板的前3阶近似振动频率、临界分岔值,表明整体运动可使柔性多体系统中的柔性构件产生动力软化效应;进一步采用假设模态法分析了板的后屈曲近似解,分别得到了从稳定平凡解失稳分岔形成的稳定的对称后屈曲解及其二次分岔产生的非对称后屈曲解,以及从不稳定平凡解分岔产生的不稳定的反对称后屈曲解。

DESIGN AND APPLICATION OF DYNAMIC MONITORING AND VISUALIZATION MANAGEMENT INFORMATION SYSTEM OF KARST LAND ROCKY DESERTIFICATION

In order to study the spatial-temporal change and environmental management of regional karst LUCC (land use and land cover change) and its causative environmental effect-rocky desertification by integrating qualitative analysis and quantitative analysis, and relying on RS, GIS and GPS (3S) techniques, karst land rocky derification dynamic monitoring and visualization management information system (KLRD.DMVM.IS) is framed, which includes design aim and structure model, function design, database design and model system design. The model system design gives priority to dynamic monitoring, drive force diagnosis, comprehensive evaluation and decision support of karst rocky desertification. From the viewpoint of model type, mathematic expression and its meaning, the dynamic monitoring models are concretely devised to reflect the spatial and temporal changing features and the trend of karst LUCC and rocky desertification. Taking Du'an Yao Autonomic County of Guangxi as an example, the KLRD.DMVM.IS is systematically analyzed in the application of the process and trend of karst LUCC and rocky desertification in Du'an County, and it provides the technical support for the study on karst land rocky desertification.

Quantitative analysis of influence of α-Al(MnFeCr)Si dispersoids on hot deformation and microstructural evolution of Al-Mg-Si alloys

The microstructural evolution of AA6061 and Mn-bearing Al-Mg-Si-Cu alloys was studied by compression tests that were carried out between 300 and 500 °C with a wide range of strain rates. Compared to the AA6061 alloy, the large amount of α-Al(MnFeCr)Si dispersoids in the Mn-bearing alloy yielded a significant increase in the flow stress under all deformation conditions. The effects of the deformation parameters on the evolution of the microstructure were studied using electronic backscatter diffraction measurements. The predominant softening mechanism of both alloys was dynamic recovery. The presence of α dispersoids in Mn-bearing alloys effectively refined the size of substructures with misorientation angles in the range of 2°-5°, which retarded the dynamic recovery. To predict the subgrain size under various deformation conditions, the threshold stresses that were caused by α dispersoids were calculated by the modified Orowan equation and incorporated into a conventional constitutive equation. The subgrain size that was predicted by the modified constitutive equation showed satisfactory agreement with the experimental measurements.

Analytical solutions of stress and displacement in strain softening rock mass around a newly formed cavity

The closed form solutions of the stress and displacement in strain softening rock mass around a newly formed cavity are derived with a three step-wise elasto-plastic model. Hoek-Brown criterion is adopted as the yielding criterion of rock mass. Damage factors are proposed to account for degradation of the material parameters to reflect the degree of strain softening. The surrounding rock mass around the cavity is divided into three regions: elastic region, strain softening region and residual state region. The analytical solutions of stress, strain, displacement and radius of each region are obtained. The effects of the strain softening and shear dilatancy behavior on the results are investigated with parametric studies. The results show that the radii of the residual state region and strain softening region in the surrounding rock mass with higher damage degree are larger. The radii of the residual state region and strain softening region are 1-2 times and 1.5-3 times of the cavity radius, respectively. The radial and tangential stresses decrease with the increase of the damage factor. The displacement of the cavity wall for the case with maximum plastic bulk strain is nearly twice than that with no dilation. Rock mass moves more toward the center for the case with larger damage factor and shear dilation. The area of the plastic region is larger when the damage factors are considered. The displacements in the surrounding rock mass increase with the increase of the damage factors and shear dilation factors. The solutions can be applied to the stability analysis and support design of the underground excavation.

Vertical dynamic response characteristics of single pile in non-homogeneous soil layers

A computational method and a mechanical model for evaluating the vertical dynamic harmonic response characteristics of a single pile embedded in non-homogeneous soil layers and subjected to harmonic loadings were established based on a certain assumption and the improved dynamic model of beam-on-Winkler foundation by using the principle of soil dynamics and structure dynamics. Both non-homogeneity of soil strata and softening effect of soil layer around the pile during vibration were simultaneously taken into account in the proposed computational model. It is shown through the comparative study on a numerical example that the numerical results of dynamic response of the single pile computed by the proposed method are relatively rational and can well agree with the numerical results computed from the well-known software of finite element method. Finally the parametric studies were conducted for a varied range of main parameters to discuss the effects of relevant factors on dynamic responses of the single pile embedded in non-homogeneous layered soils excited by harmonic loading with different frequencies.

Modeling of Soot Formation in Gas Burner Using Reduced Chemical Kinetics Coupled with CFD Code

A computational study of soot formation in ethylene/air coflow jet diffusion flame at atmospheric pres-sure was conducted using a reduced mechanism and soot formation model. A 20-step mechanism was derived from the full mechanism using sensitivity analysis,reaction path analysis and quasi steady state(QSS) approximation. The model in premixed flame was validated and with computing savings in diffusion flame was applied by incor-porating into a CFD code. Simulations were performed to explore the effect of coflow air on flame structure and soot formation. Thermal radiation was calculated by a discrete-ordinates method,and soot formation was predicted by a simple two-equation soot model. Model results are in good agreement with those from experiment data and detailed mechanism at atmospheric conditions. The soot nucleation,growth,and oxidation by OH are all enhanced by decrease in coflow air velocity. The peak soot volume fraction region appears in the lower annular region be-tween the peak flame temperature and peak acetylene concentration locations,and the high soot oxidation rate due to the OH attack occurs in the middle annular region because of high temperature.

微合金化高锰奥氏体钢静态再结晶行为的模拟

在热轧过程中，奥氏体再结晶决定了晶粒尺寸的变化和应变的累积程度，因此，用再结晶来控翩最终产品的微观组织扣力学性能。但是现在还缺乏试验数据和模型来描述高锰钢的再结晶动力学，并且现有数据和模型还没有考虑到钢中的C、Mn等合金元素对再结晶动力学的影响。本研究的目的是提出一个定量模型来描述静态再结晶动力学和计算再结晶晶粒尺寸。这个模型能够适用于较宽成分的高锰钢。为了得出这个模型，我们也应用了以前关于（20—30％）Mn-（0—1．5％）Al-（0．2-1%）C钢的研究结果。另外，还做了一些新的试验来确定变形条件对静态软化动力学和再结晶晶粒尺寸的影响。高锰钢的静态再结晶动力学遵循阿夫拉米定律，高锰钢的阿夫拉米指数n取决于温度，并且比低碳钢的阿夫拉米指数小。我们观察到50％软化率的时间（t0.5）取决于碳成分，并且把这一因素纳入到t0.5的计算公式中，提出了一个根据变形条件来计算再结晶晶粒尺寸的回归公式。

A nonlinear explicit dynamic GBT formulation for modeling impact response of thin-walled steel members

A nonlinear explicit dynamic finite element formulation based on the generalized beam theory(GBT)is proposed and developed to simulate the dynamic responses of prismatic thin-walled steel members under transverse impulsive loads.Considering the rate strengthening and thermal softening effects on member impact behavior,a modified Cowper-Symonds model for constructional steels is utilized.The element displacement field is built upon the superposition of GBT cross-section deformation modes,so arbitrary deformations such as cross-section distortions,local buckling and warping shear can all be involved by the proposed model.The amplitude function of each cross-section deformation mode is approximated by the cubic non-uniform B-spline basis functions.The Kirchhoff s thin-plate assumption is utilized in the construction of the bending related displacements.The Green-Lagrange strain tensor and the second Piola-Kirchhoff(PK2)stress tensor are employed to measure deformations and stresses at any material point,where stresses are assumed to be in plane-stress state.In order to verify the effectiveness of the proposed GBT model,three numerical cases involving impulsive loading of the thin-walled parts are given.The GBT results are compared with those of the Ls-Dyna shell finite element.It is shown that the proposed model and the shell finite element analysis has equivalent accuracy in displacement and stress.Moreover,the proposed model is much more computationally efficient and structurally clearer than the shell finite elements.

Multi-Physics CFD Simulations in Engineering

Nowadays Computational Fluid Dynamics （CFD） software is adopted as a design and analysis tool in a great number of engineering fields. We can say that single-physics CFD has been suffciently matured in the practical point of view. The main target of existing CFD software is single-phase flows such as water and air. However, many multi-physics problems exist in engineering. Most of them consist of flow and other physics, and the interactions between different physics are very important. Obviously, multi-physics phenomena are critical in devel- oping machines and processes. A multi-physics phenomenon seems to be very complex, and it is so difficult to be predicted by adding other physics to flow phenomenon. Therefore, multi-physics CFD techniques are still under research and development. This would be caused from the facts that processing speed of current computers is not fast enough for conducting a multi-physics simulation, and furthermore physical models except for flow physics have not been suitably established. Therefore, in near future, we have to develop various physical models and ef- ficient CFD techniques, in order to success multi-physics simulations in engineering. In the present paper, I will describe the present states of multi-physics CFD simulations, and then show some numerical results such as ice accretion and electro-chemical machining process of a three-dimensional compressor blade which were obtained in my laboratory. Multi-physics CFD simulations would be a key technology in near future.

钒微合金化对高锰TWIP钢热加工行为的影响

重点研究钒微合金化高锰（20%~30%）TWIP钢的静态软化和应变诱导析出行为,考察了不同钒含量（0.1%、0.2%）和碳含量（0.2%、0.6%、1%）的影响,目标是确定钒在热轧后还能有进一步析出强化作用的条件（如：成分、热加工参数）。在700~1100℃温度范围内进行了双道次扭转试验,还对卷取进行了模拟（从700℃到550℃）。采用先进的分析方法,如通过EBSD来确定晶粒尺寸和再结晶分数,采用TEM来分析析出物。结果表明,在热加工温度范围内,钒的析出相对迟缓,而且只在20%Mn-0.6%C-0.2%V或30%Mn-1%C-0.1%V的成分条件下发生。将碳含量降低到0.2%时,只在650℃和700℃模拟卷取后才能观察到析出物。另外,在有应变诱导析出发生的情况下,回复、再结晶和应变诱导析出之间有着复杂的相互影响。静态再结晶被明显推迟,导致回复对软化动力学具有重要影响。