基于GPS和GRACE数据的三维地表形变的比较及地球物理解释

GPS技术能以高空间和高时间分辨率监测地表形变.但由于测量原理的不同,GPS监测的地表形变与GRACE存在差异.本文比较了ITRF2008-GPS残差序列与基于CSR的RL05版本的GRACE球谐系数的地表形变序列的差异.结果表明,GPS和GRACE的周年变化在高程方向上具有较好的一致性,但水平方向的差异明显.重点分析了影响GPS/GRACE地表形变差异(尤其是水平方向)的三个因素:不同GPS站时间序列间的不确定性,热弹性形变和区域形变.GPS站地表形变本身的不确定度在一定程度上导致了GPS/GRACE间的差异(特别是水平方向).结合热弹性形变理论指出,由温度变化引起的热弹性形变也是导致GPS/GRACE的南北方向差异的主要原因之一.因此利用GPS数据研究地表质量负载时,必须消除热弹性形变的影响.区域负载对GPS/GRACE水平方向差异的影响也是不可忽略的,特别是对欧洲区域.

地球表面季节性形变的物理成因

地表形变运动的成因探索对环境监测、气候变化研究以及高精度地球参考框架维持都具有重要意义,主要讨论了地球表面非构造季节性运动的物理因素。首先介绍了两个已经明确了的激发机制:由大气、海洋、陆地水、雪、冰以及植被等变化引起的表面质量重力负荷,是地表季节性形变的主要激发源,可以解释40%~50%的垂向和15%~20%的水平向地表季节性形变;除此之外,地表温度变化引起的热弹性形变对GPS台站观测到的周年位移也存在激发作用,在垂向和水平方向的贡献率分别为7%和8%~9%。其次探讨了地表三维季节性形变的潜在物理机制,现有的理论证明和区域性的观测结果均表明,由地下水含量变化引起的孔隙弹性负荷极有可能对地表形变存在贡献。孔隙弹性形变的情况不同于传统水文负荷,却与热弹性效应类似,可以通过改进现有的热弹性形变模型,并将其应用到陆地水系统,拓展出全球尺度的孔隙弹性形变模型,进一步补充解释地表三维(尤其是横向分量)季节性形变。

陕西乾陵台地球动力学观测硐室的红外热成像

以陕西乾陵台为例,采用红外热像仪对引硐、NS和EW向硐室衬砌的温度进行测量和热成像。结果表明:引硐为高温段,随着不断深入,温度以近线性的趋势从20.7℃下降至14.8℃;NS向硐室温度比EW向略高,平均分别为13.5℃和13.1℃,但二者整体变化皆稳定均匀。各区段内温度存在小幅的波动现象,某些局部区域个别测点的温度较离散;而同一测点处衬砌和空气的温度并不一致,存在较大差异。硐室E端处的热像图显示顶拱的温度普遍高于侧壁。

小型断路器双金属片瞬时热分布研究

研究了双金属片瞬时温升分布。采用Ansys仿真软件建立了双金属片的有限元模型。模拟了双金属片在电流激励下的发热过程,得到了双金属片的瞬时温度分布规律和瞬时形变,同时完成了相应的温升实验研究。对比分析仿真和实验结果,得到仿真和实验的温度最大误差为1.2 K,验证了仿真方法的正确性,可为产品的优化设计提供理论依据。

温度变化对中国大陆三维周年位移的影响

除了地表质量重新分布外,地表温度变化是影响地表周年变化的另一重要成因。本文利用全球温度变化数据,基于三维全空间热弹性形变模型,计算温度变化在中国大陆引起的地表热弹性形变,并讨论它对中国大陆三维周年位移的影响。结果表明,温度变化引起的地表周年变化振幅在毫米量级。中国大陆构造环境监测网络(简称:陆态网络)GPS台站受地表温度变化影响最大的台站是HLAR(海拉尔),东向、北向以及垂向的周年振幅矢量和为~2.293mm;影响最小的台站是HIYS(永暑礁),东向、北向以及垂向的周年振幅矢量和为~0.177mm。为了说明温度变化对地表周年形变的影响,本文联合GRACE以及物质负荷模型(MODEL)研究中国大陆地表三维周年位移。考虑温度变化后的MODEL、GRACE获取的地表周年形变在东向、北向、垂向的周年信号分别改进了6%、6%、2%;16%、5%、15%。结果表明,温度变化是物质负荷以外引起大陆地表形变的重要因素。

Fabrication of flatten grooved-sintered wick heat pipe

With the rapid rising of heat flux and reduction of heat dissipating space of microelectronic devises, flattened sintered heat pipe has become an ideal conducting element of use in the electronic cooling field. A manufacturing technology named phase change flattening process is presented to fabricate the flattened grooved-sintered wick heat pipe （GSHP for short）. Deformation geometry of flattened GSHP and the elasto-plastic deformation of flattening process are analyzed theoretically and verified by experiments. The results show that the vapor pressure inside sintered heat pipe during flattening process is determined by the saturated vapor pressure equation; the width and vapor area of flattened heat pipe change greatly as the flattening proceeds; the maximum equivalent strain distributes at the interface between wick and vapor in the fiat section; the buckling phenomenon can be well eliminated when the flattening temperature reaches 480 K; phase change flattening punch load increases with flattening temperature and displacement.

Superelastic properties of nanocrystalline NiTi shape memory alloy produced by thermomechanical processing

Effects of thermomechanical treatment of cold rolling followed by annealing on microstructure and superelastic behavior of the Ni50Ti50 shape memory alloy were studied.Several specimens were produced by copper boat vacuum induction melting.The homogenized specimens were hot rolled and annealed at 900°C.Thereafter,annealed specimens were subjected to cold rolling with different thickness reductions up to 70%.Transmission electron microscopy revealed that the severe cold rolling led to the formation of a mixed microstructure consisting of nanocrystalline and amorphous phases in Ni50Ti50 alloy.After annealing at 400°C for 1 h,the amorphous phase formed in the cold-rolled specimens was crystallized and a nanocrystalline structure formed.Results showed that with increasing thickness reduction during cold rolling,the recoverable strain of Ni50Ti50 alloy was increased during superelastic experiments such that the 70%cold rolled-annealed specimen exhibited about 12%of recoverable strain.Moreover,with increasing thickness reduction,the critical stress for stress-induced martensitic transformation was increased.It is noteworthy that in the 70%cold rolled-annealed specimen,the damping capacity was measured to be 28 J/cm3 that is significantly higher than that of commercial NiTi alloys.

Thermoelastoplastic Deformation Analysis of Electromechanical Equipments under Electrocaloric Shock

A coupled thermomechanical model is presented to investigate the thermoelastoplastic deformation mechanism of electromechanical equipments under the condition of electrocaloric shock. In the coupling model, differentiating from the previous analyzing viewpoint that looked upon deformation work as additional heat source, temperature-field equation is established by considering the weakening role of deformation work on the intensity of internal heat source; in the process of setting up displacement-field equation, G-derivative of nonlinear functional is introduced into the traditional theory of elastoplastic finite deformation to simplify the expression of structural stiffness; stress-field equation is constructed by using the least square method to improve the stress solution obtained by constitutive equation. The presented model is converted into finite element program to simulate deforming process of 3-D structures with temperature-dependent material properties. As an example, thermal deformation analysis of Shanghai metro cars’ brake resistor is performed and compared with experimental results for illustrating the validity of the presented model.

Thermoelastohydrodynamic behaviour of inclined-ellipse dimpled gas face seals

The thermoelastohydrodynamic performance of an inclined-ellipse dimpled gas face seal is analyzed. The pressure distributions of the gas film and temperature fields of the seal rings and gas film are presented considering thermal and elastic distortions.Then, the influences of texturing parameters, including dimple inclination angle and dimple depth, on sealing performance are investigated under different operating parameters such as rotational speeds and seal pressures. The results show that face distortions lead to a decrease in the hydrodynamic effect at high rotational speed. The analysis shows that the opening force can decrease by more than 50% as the rotational speed increases from 0 to 35000 r min^(-1). The influence of face distortion on the seal performance, such as opening force and leakage characteristic, gradually increases with the rotational speed.

On Plane Stress State and Stress Free Deformation of Thick Plate with FGM Interface under Thermal Loading

This paper demonstrates the plane stress state and the stress free thermo-elastic deformation of FGM thick plate under thermal loading.First,the Sneddon-Lockett theorem on the plane stress state in an isotropic infinite thick plate is generalized for a case of FGM problem in which all thermo-mechanical properties are optional functions of depth co-ordinate.The proof is based on application of the Iljushin thermo-elastic potential to displacement type system of equations that reduces it to the plane stress state problem.Then an existence of the purely thermal deformation is proved in two ways:first,it is shown that the unique solution fulfils conditions of simultaneous constant temperature and linear gradation of thermal expansion coefficient,second,proof is based directly on stress type system of equations which straightforwardly reduces to compatibility equations for purely thermal deformation if only stress field is homogeneous in domain and at boundary.Finally,couple examples of application to an engineering problem are presented.