The analysis of cylindrical shell roofs with post tensioned edge beams

A new characteristic equation for cylindrical shell roofs is developed, together with a method for obtaining the solution and its derivatives. Post tension is introduced into the edge beam by shearing forces varying linearly from a maximum at the transverse to zero at the quarter points. The Fourier series for this converges rapidly. An end correction is then made to restore the post tension to the end of the edge beam and obtain compatibility of strain with the shell edge. The method is compared with experimental results on a model shell and with the results of a finite element program.     

脆塑性岩石破坏后区应力跌落效应数值模拟

采用三轴试验和数值模拟研究了岩石类脆塑性材料的应力跌落效应,并用塑性流动因子λ来描述应力跌落效应。为简化计算,给出了一种应力陡降过程中伴随的非零应变增量的工程近似处理方法,基于此针对性地编制了处理脆塑性材料应力跌落的有限元分析程序代码。数值模拟结果验证了塑性流动因子λ以及该近似处理方法的有效性。     

经历不同高温后砂岩的动态力学特性实验研究

运用RX3 -20 -12型箱式电阻炉将砂岩试样分别加热至100、200、400、600、800和1 000℃,然后自然冷却至常温,制成经历不同温度的砂岩试件。运用直径为100mm的分离式Hopkinson压杆装置,用薄圆形紫铜片作为波形整形器,以不同弹速轴向冲击砂岩试样,测试经历不同温度后砂岩试样在不同冲击荷载下的动态力学性能,得出了砂岩的应力-应变曲线及各自的破坏形态。结果表明：常温下砂岩的动态压缩破坏的应力-应变曲线具有明显的4阶段特征,但经历100~400℃作用的砂岩应力-应变曲线的平台段消失,温度继续升高时平台段又重新出现;砂岩的峰值应变随温度升高而升高,动态压缩强度也随温度升高而升高,但在800℃以后陡然下降;砂岩的动态压缩破坏形态受温度和冲击荷载的共同影响,冲击荷载越大破碎程度越大,而且破坏过程总是由外层向内芯发展。

     

Stability and extremum principles for post yield analysis of finite plasticity

The post yield behavior of rigid-perfectly plastic solids at the collapse load is studied based on the finite deformation theory. By using the general duality theory developed by Gao-Strang (1989), a global stability criteria is proposed and a pair of dual extremum principles, expressed in terms of displacements, displacement rates and the Kirchhoff stresses are established for plastic collapse analysis. It is proved that under large deformations, the existence of the plastic limit state at the collapse load depends on the directional derivative of a so-called complementary gap function. The application to the nonlinear plastic collapse theory yields a pair of dual bounding theorems for limit loading factor associated with any transient displacement of the deformed body when the global extremum criteria are satisfied. Dedicated to Professor Y.K. Cheung on the occasion of his 60th birthday     

Laboratory observation of nonlocal dispersion

This work presents the results of a one-dimensional experimental investigation of contaminant transport in heterogeneous porous media. The usual transport equations fail to adequately predict dispersion in such systems, and new theories to account for the distinctions have not yet been examined experimentally. We use a one-dimensional porous media which is heterogeneous on the scale of observation to determine if the phenomena predicted by the new theories are observable.The experimental media are constructed from distinct layers of spherical glass beads packed into cylindrical columns of Lucite. Flow was in the direction perpendicular to the layers. Dispersion was measured by recording the concentration of a chloride tracer as a function of time and position. The scale of measurement was finer than the scale of the heterogeneity. The results show that the mixing between miscible fluids was affected by transitions in the system parameters, before the transitions were encountered by the mixing zone. This newly observed phenomenon has been interpreted as a nonlocal effect, and it begins to verify the new predictive theories.     

On the calculation of wall temperatures in the post dryout heat transfer region

A non-equilibrium post dryout heat transfer model for calculating the wall temperature distribution in vertical upflows is presented in this study. The model is based upon the three path heat transfer formulation developed by MIT researchers (Laverty & Rohsenow 1964, Forslund & Rohsenow 1968, Hynek et al. 1969 and Plummer et al. 1974) that involves heat transfer from wall to vapor, from wall to droplets in contact with the wall and from vapor to liquid droplets in the vapor core. Downstream gradients for the bulk vapor temperature, vapor quality, droplet size and vapor velocities are identical to those used by Hynek et al. (1969) and Plummer et al. (1974). Conditions at the dryout location are calculated using a modified version of a technique developed by Hynek et al. (1969).A procedure for determining an average droplet diameter based on a size distribution is introduced. Migration of droplets through the boundary layer and droplet deposition flux are predicted with the model of Gani? & Rohsenow (1979). Heat transfer from the wall to the impinging liquid droplets is calculated with a correlation by Holman & McGinnis (1969). Mechanisms contributing to wall to droplet heat transfer are identified as (a) droplet-wall contact, (b) intensive droplet evaporation inside the boundary layer, and (c) destruction of the boundary layer due to droplet migration to, and rebound from, the hot surface. The significance of the average droplet size and size distribution is demonstrated through its control over the free stream evaporation and droplet deposition rates.Predicted uniform heat flux wall temperature profiles for water, nitrogen and freon 12 are in good agreement with the data of Era et al. (1966), Bennett et al. (1967), Forslund & Rohsenow (1968), Ling et al. (1971), Groeneveld (1972) and Janssen & Kervinen (1975).     

Combining field-modulating electroosmotic vortex and insulating post to manipulate particles based on dielectrophoresis

The dielectrophoretic technology has been one of the most frequently applied microfluidic technologies to manipulate particles. The way of a combination of controlled electroosmotic micro-vortices and dielectrophoresis to manipulate particles of different sizes was proposed in our previous work. However, the thickness of the modulating electrode is neglected. In practice, when the thickness of the modulating electrode increases, the channel flux increases, while the ability of the vortex to capt...     

Analysis of dynamical buckling and post buckling for beams by finite segment method

IntroductionThe stability or dynamical buckling of structures is the parametrically exacted vibration ofstructures,and itis a nonlinear vibration problem[1].Dynamical stabilityof beams was studiedusing Galerkin variation method by Russian scholar,and B.B.…     

浅谈力学类新教师如何适应教学岗位

以理论力学、材料力学课程为例，从课前备课、课堂讲解两个方面谈新参加工作的教师如何适应教学岗位．     

Aerosol observation in Fengtai area, Beijing

Measurements of aerosol number concentration and particulate matter with diameter less than 10μm (PM10) mass concentrations of urban background aerosols were performed in Fengtai area, Beijing in 2006. Black carbon (BC) was collected simultaneously from the ground and analyzed to determine the particulate matter components. To satisfy the interest in continuous monitoring of temporal and spatial distribution of aerosols, the relationship between extinction coefficient (visibility) measured by lidar remote sensing and the aerosol number concentration measured from the ground was derived by using statistical method. Vertical particle number concentration profile within the planetary boundary layer could be inversed through the lidar data as well as the statistical relation.     

Aerosol observation in Fengtai area, Beijing

Measurements of aerosol number concentration and particulate matter with diameter less than 10 μm （PM10） mass concentrations of urban background aerosols were performed in Fengtai area, Beijing in 2006. Black carbon （BC） was collected simultaneously from the ground and analyzed to determine the particulate matter components. To satisfy the interest in continuous monitoring of temporal and spatial distribution of aerosols, the relationship between extinction coefficient （visibility） measured by lidar remote sensing and the aerosol number concentration measured from the ground was derived by using statistical method. Vertical particle number concentration profile within the planetary boundary layer could be inversed through the lidar data as well as the statistical relation.     

Laboratory observation of slow movements in rocks

It is established that the development of a localized plastic strain during compression of samples of rocks (sylvinite, marble, and sandstone) deformed by different micromechanisms has an autowave character. It is shown that the velocity of propagation of autowaves arising in the samples under compression is 10^?5 to 10^?4 m/s (0.3 to 3.0 km/g) and is close to the velocity of slow waves observed in the Earth??s crust after earthquakes or rockbursts.     

High-speed observation of ultrahigh-speed submerged water jets

Some peculiar phenomena occur around ultrahigh-speed submerged water jets accompanied by very severe cavitation erosion. Using the flow visualization technique with a xenon flash, the water jets were carefully observed, and the spatial distributions of highly erosive impulsive pressures around the jets were measured by means of a pressure-sensitive film technique. The effects of the injection pressure and the nozzle configuration are systematically clarified. Thus, the characteristics and structures of ultrahigh-speed submerged water jets are clearly shown.     

Scientific post hoc and in situ visualisation of high-order polynomial solutions from massively parallel simulations

This paper presents two recent numerical tools developed respectively to perform traditional post-processing and more advanced in situ processing of high-order polynomial data generated by massively parallel finite element codes. For post-processing and visualisation of high-order solutions, we present a new ParaView plugin that integrates Gmsh used as an external library. This plugin therefore combines respectively ParaView's scalability in parallel and Gmsh's ability to apply h-refinement of the initial mesh followed by solution interpolation on the resulting visualisation grid, thus enabling parallel visualisation of any arbitrary high-order polynomial solutions in client–server mode. In a second stage, this capacity has been extended to an in situ interface based on the Catalyst library which enables in situ analysis and visualisation of high-order solutions. These new capacities are demonstrated with the visualisation of high-order solution of the unsteady flow generated by a discontinuous Galerkin method for an unsteady turbomachinery application.     

GPS/GALILEO组合系统观测数据的模拟

针对因无法得到GALILEO原始观测数据而限制了对GPS/GALILEO组合定位深入研究的问题,通过分析GALILEO卫星运动情况,仿真出GALILEO卫星历书文件;参照GPS定轨定位中的主要误差,分别采用Klobuchar模型和Hopfield模型对电离层和对流层误差进行了模拟.利用已知任意历元卫星的三维位置,恢复该历元卫星可观测到的卫星信号,最后生成RINEX观测文件.生成的GPS/GALILEO数据能够较好地反映出观测的实际情况,为GPS/GALILEO组合定位的研究提供了数据基础.     

Effect of random perturbations on adaptive observation techniques

An observation sensitivity (OS) method to identify targeted observations is implemented in the context of four‐dimensional variational (4D‐Var) data assimilation. This methodology is compared with the well‐established adjoint sensitivity (AS) method using a nonlinear Burgers equation as a test model. Automatic differentiation software is used to implement the first‐order adjoint model (ADM) to calculate the gradient of the cost function required in the 4D‐Var minimization algorithm and in the AS computations and the second‐order ADM to obtain information on the Hessian matrix of the 4D‐Var cost that is necessary in the OS computations. Numerical results indicate that the observation‐targeting is particularly successful in reducing the forecast error for moderate Reynolds numbers. The potential benefits of the OS targeting approach over the AS are investigated. The effect of random perturbations on the performance of these adaptive observation techniques is also analyzed. Copyright © 2011 John Wiley & Sons, Ltd.