致密油藏直井体积压裂压力分析模型

致密储层基质和裂缝一般表现为强应力敏感性,同时由于储层的致密性,基质和裂缝经常会表现为非稳态窜流特征,影响井底压力曲线的形态和特征,进而影响解释结果。目前国内外尚缺少同时考虑应力敏感及非稳态窜流的井底压力分析模型。参考典型致密油藏体积压裂直井的微地震监测数据,设计体积压裂直井渗流物理模型,同时考虑应力敏感和非稳态窜流,建立体积压裂直井井底压力数学模型并求解,进而获得井底压力的双对数曲线特征。研究结果表明:应力敏感系数αD越大,压力导数曲线上翘幅度越大,压裂未改造区致密油径向流动阶段越不明显;非稳态窜流系数λm越小,窜流出现时间越晚,窜流阶段的下凹幅度越大,窜流渗流过程持续时间越长,压裂区域的裂缝径向渗流过程越弱。该井底压力分析模型应用表明,相较于未考虑应力敏感及非稳态窜流的模型,更能准确地确定压裂区域的半径及相关储层参数,提高致密油藏直井体积压裂相关参数的解释精度,故可推广到致密储层参数反演或试井解释分析中。

基于ABAQUS的半遮帘式板桩码头有限元分析

为了分析出改造后的半遮帘式板桩码头的应力状态,结合某码头改造工程,应用ABAQUS建立了有限元二维模型和三维模型,对半遮帘式板桩码头进行受力分析,得出设置半遮帘桩可以大幅减小作用在板桩墙后的土压力,从而减小板桩墙跨中弯矩的结论。在计算过程中发现,应用平行墙理论计算前板桩墙在遮帘桩范围内的土压力时,应将其中静止土压力系数调整为主动土压力系数;计算前板桩墙弯矩时,二维模型和三维模型的计算结果趋势一致,且数值相差很小,在5%以内。

“压力-状态-响应”下乡村营建与大型节事的作用机制与韧性策略——以杭州亚运会为例

大型节事作为乡村转型触媒的同时,也容易引发脆弱性风险。针对这一问题,以杭州第19届亚运会为例,通过“压力-状态-响应”分析模型,探讨了大型节事对乡村营建的影响及其带来的挑战和机遇,揭示了乡村转型与大型节事之间的作用机制。研究发现,大型节事的扰动在与乡村既有的发展状态作用后,会引发乡村营建在事前和事后的响应举措,并反馈调控节事扰动。研究提出了针对乡村节事空间营建的韧性策略,包括全生命周期规划、地域特征导则和多元主体参与运维,旨在提供大型节事扰动下乡村的营建法则与实施路径。

Numerical Analysis of Finite Deformation of Overbroken Rock Mass in Gob Area Based on Euler Model of Control Volume

The overbroken rock mass of gob areas is made up of broken and accumulated rock blocks compressed to some extent by the overlying strata. The beating pressure of the gob can directly affect the safety of mining fields, formarion of road retained along the next goaf and seepage of water and methane through the gob. In this paper, the software RFPA＇2000 is used to construct numerical models. Especially the Euler method of control volume is proposed to solve the simulation difficulty arising from plastically finite deformations. The results show that three characteristic regions occurred in the gob area： （1） a naturally accumulated region, 0-10 m away from unbroken surrounding rock walls, where the beating pressure is nearly zero; （2） an overcompacted region, 10-20 m away from unbroken walls, where the beating pressure results in the maximum value of the gob area; （3） a stable compaction region, more than 20 m away from unbroken walls and occupying absolutely most of the gob area, where the beating pressures show basically no differences. Such a characteristic can exolain the easy-seeoaged “O”-ring phenomena around mining fields very well.

An Analytical Approach for Assessing the Collapse Strength of an Unbonded Flexible Pipe

This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA model and a number of test data, and showed reasonably good agreement. The theoretical analysis showed that the pressure armor layer enhanced the strength of the carcass against buckling, though the barrier weakened this effect. The collapse strength of pipe was influenced by many factors such as the inner radius of the pipe, the thickness of the layers and the mechanical properties of the materials. For example, an increase in the thickness of the barrier will increase contact pressure and in turn reduce the critical pressure.

Analytical solution to rock pressure acting on three shallow tunnels subjected to unsymmetrical loads

According to the interaction of three shallow tunnels with large section, the analytical solution to rock pressure has been derived and discussed. The load model is given when the bilateral tunnels are excavated. According to the model, the stresses of three tunnels and single tunnel are calculated and compared to analyze the distribution characteristics, where the stresses are influenced by controlling factors of clear distance, covering depth and inclination angle of ground surface. The results show that, in general, the bias distribution is more serious. Therefore, it is significant to settle down the load model of three shallow tunnels so as to determine the measure of reinforcement and design the structure of support. The model and results can be used as a theoretical basis in designation and further research of the three shallow tunnels.

ELASTOPLASTIC ANALYSIS OF THICK-WALLCYLINDER CONSIDERING THE MATERIAL'S DILATANCY CHARACTER

Impermeable bentonite or its mixtures have been proposed as candidate materials to be used in the geotechnical disposal of radioactive nuclear waste. These materials are filled in the space between a canister containing radioactive nuclear waste and an underground chamber to absorb the radionuclide emitting from the canister and simultaneously retard its migration accompanying the perrneation of underground water to prevent the surrounding environment from po1lution. On the basis of the established elastoplastic strain-hardening mechanical model considering the material’s dilatancy character,the authors carry out the stress-strain analysis of a thick-wa1l cylinder in a plane strain state subJected to a pressure difference between internal and external pressures. The analysis may be expected to be a theoretical basis for developing a coupled shear and permeability test apparatus for conducting a permeability test along a sheared plane in a specimen. The apparatus will be used to study the effects of shear strain on the variation of geotechnical materials’ permeability coefficient in order to evaluate the influence of shear strain caused by nonuniform deformation and/or earthquake on the long-term safety of the disposal system of radioactive nuclear waste. The theoretlcal analysls methods in this paper can be directly spread to the analysis of the deformation and stability of tunnels or roadways driven in soft soils or high moisture-bearing soft rocks.

Limit analysis method for active earth pressure on laggings between stabilizing piles

Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between piles. Evaluating the earth pressure acting on laggings is of great importance in design process.Since laggings are usually less stiff than piles,the lateral pressure on lagging is much closer to active earth pressure. In order to estimate the lateral earth pressure on lagging more accurately,first,a model test of cantilever stabilizing pile and lagging systems was carried out. Then,basing the experimental results a three-dimensional sliding wedge model was established. Last,the calculation process of the total active force on lagging is presented based on the kinematic approach of limit analysis. A comparison is made between the total active force on lagging calculated by the formula presented in this study and the force on a same-size rigid retaining wall obtained from Rankine's theory. It is found that the proposed method fits well with the experimental results.Parametric studies show that the total active force on lagging increases with the growth of the lagging height and the lagging clear span; while decreases asthe soil internal friction angle and soil cohesion increase.

Study on cogging force of permanent magnet linear synchronous motor

Presented the methods to obtain the cogging force of permanent magnet linear synchronous motors(PMLSMs), analyzed the characteristics of the cogging force, and provided a basis for reducing the effect of the cogging force. 2-dimensional finite element method(2D FEM) was used to solve the whole motor when its mover was at dif- ferent position, so that the relation was derived between the cogging force and the mover position. The analysis results show that the cogging force between the two ends of the primary iron-core and the secondary permanent magnets (PMs) is sinusoidal function of the mover position under certain conditions only. Two proposed methods, namely direct and indirect methods, are applied to calculate the cogging force between the primary iron-core teeth and the secondary PMs. The agreement of the two methods is validated.

Nonlinear static response of piezoelectric plates considering electro-mechanical coupling

Nonlinear static analysis of piezoelectric plates has been carried out using nonlinear finite element method considering electro-mechanical coupling,The geometrical nonlinearity has been taken into account and electric potential is assumed to be quadratic across the plate thickness,The governing equations are obtained using potential energy and Hamilton's principle that includes elastic and piezoelectric effects.The finite element model is derived based on constitutive equation of piezoelectric material accounting for coupling between elasticity and electric effect using higher order plate elements,Results are presented for piezoelectric plate under different mechanical boundary conditions,Numerical results for the plate are given in dimensionless graphical forms.Effects of boundary conditions on linear and nonlinear response of the plate are also studied.The numerical results obtained by the present model are in good agreement with the available solutions reported in the literature.

Ecological Security Assessment of the Yancheng National Nature Reserve based on GIS

This study used remote sensing and GIS to analyze the landscape pattern changes in the Yancheng Nature Reserve from 1983 to 2018,established an evaluation index system based on the regional natural-socio-economic complex ecosystem security pattern,and then analyzed the spatial characteristics of ecological security changes and discusses reasons for these changes.The results show that the landscape pattern changed dramatically from natural landscape to a mixture of natural landscape and artificial landscape from 1983 to 2018 due to the intensification of human activities.At present,the ecological security status of the protected areas is not optimistic.From the perspective of the survival status of red-crowned cranes,the protected areas are suitable.However,due to the increase of human activities and policy adjustments,the habitat of red-crowned cranes is fragmented.The red-crowned crane currently gathers in localized areas such as the core area and the buffer zone.We should pay more attention to management,policy development and the environmental awareness of local residents.At the same time,it is necessary to reduce the intensity of human activities within the reserve.

Assessing the Health of Inland Wetland Ecosystems over Space and Time in China

Wetland is a unique natural landscape pattern,which provides a variety of important functions and services for human societies.With the rapid develop of the economy and accelerated urbanization,the inland wetlands are faced with series of problems,including reduced area,weakened wetland functions,and deterioration of the wetland ecosystem environment.Therefore,it is necessary to quantitatively assess the ecological health of China’s inland wetlands,which is key to the sustainable development of ecosystems.However,most assessments of wetland ecosystems only examine single wetlands or watershed wetlands,and there are few assessments of wetland health at the national level.In this paper,based on land cover data,climate data,and social and economic data,an assessment system of inland wetland health is established by using the Pressure-State-Effect-Response(PSER)model,which includes 15 assessment indicators.Analytic hierarchy process(AHP)was used to define the indicator weights.Then we assessed the ecosystem health of the inland wetlands of China in 2010 and 2018,which produced three main results.(1)Unlike ecosystem health evaluated by administrative districts,wetland ecosystem health(WEH)evaluation based on the grid could provide additional details of wetland health.(2)The area of inland wetlands increased by 16328 km^(2) in 2018 compared to 2010,and the average wetland ecosystem health index in 2018 was 3.45,compared to an index value of 3.24 in 2010.(3)In 2018,wetlands in the better,good,moderate and poor conditions represented about 26.3%,46.4%,26.9%and 0.5%of the total,respectively.These results provide a practical guide for protecting and managing wetland system resources and reliable information for land use planning and development.