大高差长输供热管线中继泵站设置分析

目的研究大高差下长输集中供热干线中继泵站的设置条件,中继泵站在供热干线中的理论设置范围,中继泵站位置对长输供热干线上各种泵扬程的影响.方法采用传统的水力计算方法和流体动态模拟分析软件(AFT Fathom10),对山西省阳城电厂拟向晋城市区供热的23 km长距离供热输送管线进行可行性分析,研究在大高差下供热管道内的压降规律.结果 AFT Fathom模拟得出管线压力曲线,中继泵站的设置条件,得出了满足工况要求的中继泵站设置范围为距供热首站3 785~10 222 m.系统循环泵扬程为97.7 m,中继泵扬程为54.6~113 m,系统总扬程为210.7 m.AFT Fathom模拟管道压力可知大高程差对管道压力有着明显的影响;水压图分析可以确定系统中各泵的扬程及运行所需总扬程,且所需总扬程保持定值.结论设置中继泵站与隔压站相结合的供热工程方案,在大高差下可以同时满足输送干线及城区一级管网的压力等级.在满足输送需求的水力工况基础上,在中继泵站设置范围内,可现场勘察选出最合适的中继泵站设置位置.

Experimental research on ultimate bearing capacity of N-joints of grouted square steel tube trusses

Cave-in failure is apt to occur in joints of trusses made of square hollow sections. In order to turn the failure mode into a strength failure mode of joint members, the idea is proposed that the chord of the truss is grouted to increase the cave-in beating capacity of a hollow tube chord. An experiment of eight specimens of N- joints made of grout-filled square steel tubes is performed. Based on the experimental study, the geometrical parameters of specimens are analyzed, and the effects of the confinement index ε, the spacing between the two web members g and the ratio of side length of the vertical web member to that of the chord β on the behavior of specimens are investigated through simulation analysis by simulation analyses, the mechanical properties and the failure an ANSYS program. Based on the test results and modes of this kind of joints are analyzed and the formulae to predict the ultimate bearing capacities corresponding to different failure modes are developed. The ultimate bearing capacity of compressive N-joints is calculated in accordance with the cave-in failure mode of a chord member; the ultimate bearing capacity of tension N-joints is calculated in accordance with the punchingshear failure mode; the ultimate bearing capacity of a chord member is calculated in accordance with the shear failure mode in normal sections.

Shear stress distribution and characteristics of deformation for shear band-elastic body system at pre-peak and post-peak

The distributed shear stress and the displacement across shear band, the evolution of plastic zones, and the load-carrying capacity of rock specimen were investigated in plane strain direct shear test according to Fast Lagrangian Analysis of Continua （FLAC）. And then the shear displacement distribution in normal direction of system composed of localized shear band and elastic rock was analyzed based on gradient-dependent plasticity. The adopted failure criterion was a composite of Mohr-Coulomb criterion, that is, the relation between tension cut-off and postpeak constitutive of rock was linear strain-softening. Numerical results show that shear stress field approximately undergoes three different stages. At first, shear stress is only concentrated in the middle of top and base of specimen. Next, shear stress in the middle of specimen tends to increase, owing to superposition of shear stresses. Interestingly, two peaks of shear stress appear far from the loading ends of specimen, and the peaks approach with the increase in timestep until elements at the center of specimen yield. Finally, relatively lower shear stress level is reached in large part of specimen except in the regions near the two ends. As flow stress decreases, the analytical shear displacement distribution in shear band based on gradient-dependent plasticity becomes steeps outside the band, it is linear and its slope tends to decrease. These theoretical results qualitatively agree with that of the present numerical predicted results. Main advantage of the analytical solution over the numerical results according to FLAC is that it is continuous, smooth and non-linear （except at elastic stage）.

Stability assessment of the freeway over the gob of coalmine

The freeway passes over the gob area of the Zaibo coalmine or its neighbor- hood when it is built. It is a noticeable problem that the construction of freeway and the underground coal mining interact, especially the deformation and destruction of the gob area of the coalmine influence the long-term stability of the freeway. In the paper, based on the actual data of the exploration about the gob area of Zaibo coalmine and the built project of the freeway,the variety rule of the coal beds below the freeway was studied by using of FEM during the process of coal mining. The statuses of the stresses and strains,the varieties of the plastic area were simulated in the whole rock mass. The characters of stresses and deformation of the gob area of the coalmine were analyzed and evaluated after the freeway built. The long-term stability of the gob area was pre- dicted. The deformation of the gob area under the freeway has not been finished, and the relative measures must be taken.

Finite layer and triangular prism element method to subsidence prediction and stress analysis in underground mining

The application of the finite layer & triangular prism element method to the 3D ground subsidence and stress analysis caused by mining is presented. The layer elements and the triangular prism elements have been alternatively used in the numerical simulation system, the displacement pattern, strain matrix, elastic matrix, stiffness matrix, load matrix and the stress matrix of the layer element and triangular prism element have been presented. By means of the Fortran90 programming language, a numerical simulation system based on finite layer & triangular prism element have been built up, and this system is suitable for subsidence prediction and stress analysis of all mining condition and mining methods. Comparing with the infinite element method, this approach dramatically reduces the size of the set of equations that need to be solved, and greatly reduces the amount of data preparation required. It not only saves the internal storage, and the computation time, but also decreases the cost.

Utilization of CO2 Injection to Improve Oil Recovery of the Handsworth Bakken Formation

The Bakken formation has become a prominent oil resource for south-east Saskatchewan, especially with the advent of horizontal well technology and new hydraulic fracturing methods. As more wells are drilled, there is a desire to determine whether there is potential for improved oil recovery and to evaluate the economic feasibility. This paper evaluates the benefit of implementing waterflooding, CO2 injection or WAG （water-alternating-gas） recovery methods for improved oil recovery of the Bakken formation. A simulation model resembling the study area was built using CMG-GEM （computer modeling group-generalized equation of state model） reservoir simulation package and a history match of the primary recovery data available was performed. Based on the simulation results, it was concluded that waterflooding had a significant influence on the oil recovery factor, although COz provided the highest increase in crude oil recovery, The capital expenditure for surface facilities and cost of injected fluid was the most economically viable for implementation of waterflooding. The WAG injection simulation results were similar to CO2 injection, except that reservoir pressure was able to be better maintained. Given that high-quality source water is available, waterflooding is the most economically feasible choice according to the simulation results obtained from this study.