Research on Mechanical Characteristics of the Cemented Sandstone Based on 3Dimensional PFC Numerical Model

Sandstone is sediment rock composed of many cemented sand particles, and corresponding particle constraint and force bearing capacity are greatly controlled by the cemented property. In order to better reflect the cemented property influencing on the mechanical characteristics of the sandstone, take the oil sandstone reservoir for instance, a numerical model based on 3Dimensional Particle Flow Code (PFC3D) considering the parallel bond model was brought forward to simulate the failure mechanism during shearing process. The sandstone cemented property is modeled based on random mathematics and advanced development of Particle Flow Code (PFC), and the relation of the stress ratio, volume strain, coordination number and bond-broken number and the axial strain is analyzed in detail, especially the contact network evolution indicated the force chain is important to transfer the external force, which verifies the feasibility of the numerical model. Based on the above PFC3D model, a series of researches on changing the cemented radius ratio, parallel bond stiffness and cemented volume of the particles have been done to clearly illuminate the importance of cemented property for the bearing capacity of the sandstone structure, which provides a scientific base for research on the failure mechanism of the sandstone under special conditions. Therefore, the above numerical method is more efficient and applicable for comparatively large scale and complex experiments, and the obtained research results can bring a new thought for the real cemented sandstone to research on its macro-micromechanical response and the structure failure mechanism, and also is significant for the sand production mechanism, sand volume prediction and sand control measures for the sandstone reservoir.     

Analysis of Mehcanical Reseponse for Different Physical Property of Reservoir Sandstone

The reservoir sandstone is the sedimentary rock with many cemented sand particles. The different physical property of the reservoir even in the same area results in different mechanical response and sand production of the sandstone. Taking two types of the reservoir sandstones as research subjects, a numerical model based on 3-Dimensional Particle-based Distinct Element (PFC3D) under cylindrical coordinate system was used to simulate the micro-micro response of the sandstone considering the given confining pressure and the oil flow rate. Meanwhile, the sanding initiation and the process of the development were analyzed. The macro stress indicated that the reservoir sandstones with weaker cemented sand particles and less percent of the cemented materials would yield and fail more easily, the sand production was initiated more easily as well. Meanwhile, the stress of the parallel bonds indicated that the reservoir sandstones with granule and less cemented materials dislodged from the sandstone more easily, and the force on the particle contact was larger and the sandstone failure was more serious.Hence, the probability of the dislodged particles flowing into the wellbore was also much more. In addition, the particle displacement and rotation indicated that the physical property of the sandstone played a significant influence on the mechanical response and the sand production, the results also agreed with the above results. Therefore, the sand mechanical response and sand production of reservoir sandstone are both different due to different physical property of the reservoir. As a result, the reliable measures of the sand prediction and sand control will be adopted based on the reservoir physical property and conditions.     

Effect of attached particles on the mechanical propertiesof dipolar chains in magnetorheological fluids

There are some particles attached to the side of dipolar chains in magnetorheological fluids. The reorganization and rupture of these chains are simulated when a tension and shear movement are applied, respectively. And the micromechanical behavior of these chains is also analyzed. It is found that the attached particles move into the chains during the tension, which increases the strain when the chain ruptures. While in shear process, attached particles introduce localized weakness in chain, which makes the chain rupture more easily and decreases the strength of the chain.     

Mechanical and Deformation Characteristicson Shield Tunnel Segment with Cracks

The 3D Goodman element is used to simulate segments' cracks in one section of shield tunnel in Guangzhou. Mechanical and deformation characteristics of segment structure responded to varied depth of cracks is analyzed in this paper. Meanwhile, research on coefficient of lateral earth pressure, soil coefficient and ground water level on mechanical and deformation characteristics is carried out. The research result shows that along with the increase of cracks' depth, the tensile stress, pressure stress reach the maximum value while the increment is not too much. However, when the depth equals to the thickness of segment, the reinforcements' tensile stress has increase sharply, even exceeded the allowable value. Moreover, the maximum number of tensile stress, horizontal and vertical convergent value of shield tunnel segment with cracks increase with the reduction of the coefficient of lateral earth pressure and soil coefficient, and increase with the increase of ground water level as well. Specific repair measure has been taken to segments' cracks in this section of shield tunnel based on the conclusions. In general, this section of shield tunnel is stable and safe now, and there is no longer new cracks appeared.     

Submicron Particles Sizing Methods and Measurement Techniques

Due to a series of wonderful characteristics, submicron particles are of high value in national economy, defense modernization and high technology fields, with wide application prospects. Submicron particle sizing methods and techniques are difficult problems in particle research field. Modern methods for particle sizing are stated and analyzed. Some problems are discussed when these methods are used for submicron particles.     

A Hypoplastic Macro-Element Model for Circular Shallow Foundations of Offshore Wind Turbines Under Combined Loading

The foundation for offshore wind turbines is subjected to vertical loading caused by structural weight and horizontal loading and moment due to wind- or wave-induced loading. Furthermore, it sustains torque from rotor blades. Based on the framework of hypoplasticity theory, the available general yield function and plastic potential function, a macro-element model for circular shallow foundations on sands under six-degree-of-freedom combined loading has been developed. In this model, to correctly reproduce the mechanical response of offshore foundations under cyclic loading, the concept of equivalent inter-granular strain is introduced into the relationship of generalized forces as well as its corresponding displacements. The performance of the proposed macro-element model is demonstrated by comparing the model predictions with available experimental data from a series of model tests.     

Effects of Vibration History on Modulus and Damping of Clay

Aiming at evaluating the effects of vibration history on dynamic characteristics of normally consolidated clay, a series of multi-cycled cyclic shear tests were conducted on 16 soil samples under consolidation pressure of 50 kPa, 100 kPa, 300 kPa and 500 kPa respectively. The experimental results reveal that, on the stage of drainage and consolidation, with the development of duration shear modulus curve ascends while damping curve descends; this trend became significant as consolidation pressure increased. The variation tends to be stable in 25 hours. When subjected to cyclic loading controlled by constant strain amplitude, both the modulus and damping of soil samples change significantly during the first 50 cycles, and then the differences become moderate afterwards, in which the damping curve acts in hyperbolical type. It is also found that there exists a clear sign of pre-straining that affects damping more significantly than modulus.     

Study on mechanical behaviors of interface with cemented soil slurry between gravel and concrete by simple shear tests

The mechanical behaviors of the interface between coarse-grained soil and concrete are investigated by simple shear tests under conditions of cemented soil slurry (clay mixed with cement grout). The results show that the relation curve between shear stress and shear strain appears stress-strain softening and shear dilatation is significant. The point of peak strength and the position when the shear dilatation occurs are related to normal stress. In addition, shear dilatation occurs before the shear stress reaches peak value. In shear failure state, with the same height, the shear displacement increases as the normal stress increases. While with the same normal stress and at the same height, the shear displacement increases as the concrete content increases. A particle flow model of simple shear test between interface between coarse-grained soil and concrete is constructed by PFC (particle flow code). The disturbed height of the sample and the main influence factors are determined by analyzing the laws of particle motion at different heights inside the sample. The PFC results show disturbed height of the sample is related to maximum particle diameter of the soil, normal stress and roughness of the interface (with or without slurry) etc. In terms of the coarse-grained soil, the shear displacement is significant in the area which is close to the interface and about 3-4 times of the maximum particle diameter, and informed the obvious shear band. Further, the thickness of the interface can be regarded as the value.     

春小麦籽粒灌浆期沉淀值动态的定量研究

以3个不同品质类型春小麦品种为材料,在设定不 同肥力和气象条件等环境因子基础上,通过建立灌浆期籽粒沉淀值动态曲线拟合方程,定量揭示籽粒沉淀值的动态与规律。结果表明,灌浆期籽粒沉淀值随时间的变化符合一元三次多项式凸性曲线,即自开花始先增后降的单峰曲线。灌浆期籽粒沉淀值的动态,不同基因型具有不同特点。高蛋白强筋、高蛋白中筋和低蛋白弱筋品种曲线峰值分别出现在开花后28 d、23 d和30 d前后。各品种沉淀值积累速度的动态特点是成熟时沉淀值高蛋白强筋品种最高,高蛋白中筋品种次之,低蛋白弱筋品种最低的主要原因。     

Joint Bearing Analysis for the Preloading Water-filled Spiral Case of Lager Hydropower Station

Spiral case is the core structure of powerhouse,therefore,it is critical to obtain its accurate stress and strain.Simplified algorithm is adopted to analyze the mechanical characteristics of preloading water-filled spiral case of a large hydropower project.The numerical results show that the adoption of preloading water-filled spiral case structure is feasible.The maximum stress of surrounding concrete mainly lies in the top of spiral case structure at various sections.The suitable internal pressure is 1.9MPa.The stress of surrounding concrete of spiral case is mainly caused by water pressure,and the effect of upper loading is limited,which is only about 5% to 24%.     

Evolvement of Plastic-loop of Fine-sandstone Under the Loading and Unloading Conditions

The deformation characteristics and the plastic-loop of the fine-sandstone is studied under the loading and(unloading) condition at the three different deformation-rates and the two different stress-levels,the results show: 1) There is really the plastic-loop in the deformation curve for the loading deformation curve is different form the unloading deformation curve.But the plastic-loop is nearly unchangeable since the second circulate loading.2) There is different for every imitational parameter between the first deformation curve and the second deformation curve at the different stress-levels and the different deformation-rates,but every imitational parameters become more and more invariable gradually since the second circulate curve.3) With the change of the deformation-rates and stress-levels,the imitational(parameters) will change with it.4) The imitational parameters are different for loading section and unloading section of the fine-sandstone deformation curve at the same circulate curve under the same deformation-rate and stress-level.     

湖南农业生态系统能值结构功能效率分析

为了探究湖南农业生态系统的能值投入产出结构功能与效率,揭示该区域人与自然资源和环境的相互关系,以能值理论为研究方法,以湖南农业2009年投入产出数据为依据,对湖南农业生态系统的能值结构、功能和效率进行实证分析。结果表明：（1）系统结构特点：湖南农业仍具有传统农业的生产特点,对劳动力、畜力的依赖性较大。工业辅助能值中,化肥对系统的贡献率最高,农业机械化水平低。工业辅助能值可更新比偏低,农业绿色能源的开发潜力和前景较大。系统产品定价偏低,忽视了自然资源和环境对农业生产的贡献,也反映出湖南农业产业链条相对短,产品附加值较低的特性。系统内部种植业和畜牧业的能值产出占绝对优势比例且其市场定价相对于林业和渔业偏低。（2）功能：该系统环境负载率虽不高,但是人口承受力超载。系统可持续发展指数为5.96,表明该系统富有活力和发展潜力,也意味着该系统经济并非常不发达、自然资源和环境的压力不是很大。（3）效率：该系统2009年的能值投入产出率略低于全国水平,表现出较明显的粗放型经济特点。因此,控制人口过快增长,转移剩余劳动力,进一步调整农业产业结构和产品结构,加强农业技术开发和利用,延长产业链,提高农业机械化和现代化水平是当前湖南农业的基本政策取向。     

Numerical Simulation of Eelastoplastic Multi-scales Model for Casting Magnesium Alloy

To realize the transforms of stress and strain and obtain the multi-scale constitutive equation across micro/meso/macro scales.strain-stress curves for magnesium alloy(AM60) and magnesium matrix are carried out with the machine MTS.By means of mixture law,mechanical property of particle is obtained.Based on the character of magnesium alloy structure,the finite element model of unit-cell included complex micro-structures is carried out.Via finite element numerical simulation of magnesium alloy unit-cell,the methodology overcome the limitation of present analytical method.Finally the multi-scale constitutive equation has been used for the analysis of the tensile stress vs. strain curve for magnesium alloy.Results show satisfactory agreement between the stress vs strain curve by the present methodology and the experimental data for AM60.     

离散元法在农业工程领域的应用进展

简述了离散元法在农业工程领域方面的研究成果,根据离散元法在农业工程领域的不同应用,分别讨论了离散元法在土壤散体颗粒、农业物料颗粒、多相流中单相介质的应用研究现状,指出了存在数量级受限,颗粒模型不精准,复杂工况制约等问题。提出今后离散元法的研究趋势:开发农业工程领域的专用离散元软件,提高颗粒群的运算效率;通过准确获取物料的细观参数,从理论基础上完善接触模型,使仿真颗粒与真实颗粒更为接近;通过离散元法软件与其他软件耦合,结合API的二次开发,拓宽离散元法在复杂散体颗粒运动仿真的应用。     

Experimental analysis of the deformation of sandstone under cyclic pore water pressure and wavelet transformation

To explore the characteristics of deformation of sandstone under cyclic pore water pressure, the experiments with different axial stresses (60%, 70% and 80% of peak intensity) of sandstone subjected to cyclic pore water loading are investigated by using MTS815 rock mechanics testing system, and irregular small deformation in deformation curve of sandstone are also processed by wavelet transformation of Matlab. The results show that with the increase of constant axial stress, fatigue deformation under cyclic pore water pressure will accelerate the failure of the sandstone. With the increase of the number of cyclic pore water pressure, the deformation evolution of the plastic-loop is illustrated as sparse-dense-sparse. The deformation curves of sandstone under cyclic pore water pressure affected by many factors are decomposed, reconfigurable processed and evaluated by using wavelet transformation, which indicates that the basic curve with optimal decomposition scale fits well with the experimental curves and reveals the deformation evolution of sandstone.     

Average surface roller pressure calculation method of roller mill

Hydraulic system pressure, contact surface between grinding roller and materials and grinding roller force of roller mill are analyzed. A new roller pressure calculation method named average surface roller pressure calculation method is proposed,and the corresponding theoretical formula is derived from three different perspectives, including roller pressure numerical calculation, stress and strain of main components and mill power through the calculation of real samples. The average surface roller and traditional average material roller pressure are compared to verify the correctness and accuracy of the proposed method. Design parameters such as the grinding roller structure, material maximum size, layer height and working pressure of the hydraulic system on the influence of roller are analyzed according to the formula of roller pressure. The research results provide theoretical basis for the selection of design parameters and the design calculation of structural strength for roller mill.     

Experiments on triaxial mechanical properties of soft coal containing gas

Taking briquette specimens composed by soft coal with outbursting trends as research object, systematic research of the influence on triaxial mechanical properties of soft coal containing gas caused by confining pressure and gas pressure is done. The results show that confining pressure can significantly affect mechanical properties of soft coal containing gas, the compression phase of soft coal containing gas is obvious and the triaxial strength is increased gradually as confining pressure is increased; the influence on elastic modulus and shape of stress-strain curve is not obvious. The triaxial strength of soft coal containing gas shows decrease trend as gas pressure is increased; the influence on strength of soft coal containing gas caused by gas pressure is obvious when the confining pressure is smaller, but it is not obvious when the confining pressure is bigger. the influence caused by gas pressure on elastic modulus and deformation of yield step is not obvious; gas pressure has not only obvious mechanical effects,but also have chemical action on soft coal containing gas; stress-strain curve of soft coal containing gas can be expressed by conic, the influence caused by gas pressure can be considered as equivalent confining pressure effects.     

Seismic Behavior of a Slope Protected by a Soil Nailing Retaining Wall during an Earthquake

The dynamic elastic plastic finite element method was used to study the seismic performance of a slope protected by a soil nailing retaining wall. On the basis of working in parallel and interaction between loess and a flexible retaining wall, a 3 D nonlinear finite element method (ADINA) also was established. Rational earthquake excitation and damping were discussed for geological engineering. Horizontal and vertical excitations were considered simultaneously in the analyses. A model capable of simulating the nonlinear static and dynamic elastic plastic behavior of soil was used to model the soil, and a bilinear elastic plastic model having hardening behavior was used to model the soil nailing. A friction element was employed to describe the soil structure interaction behavior. Our research focused on the seismic performance of the horizontal and vertical slope deformation, soil nailing axial force, and earth pressure subjected to horizontal and vertical excitations. The results show that the seismic performance of slope protected by soil nailing is good; soil nailing axial force increases after an earthquake; permanent slope displacement occurs during an earthquake; and the peak earth pressure distribution during an earthquake is similar to the earth pressure before the earthquake. These conclusions can provide references for seismic analyses and design in soil nailing engineering.     

解磷巨大芽孢杆菌液体发酵培养条件的优化

为了获得高密度培养的解磷细菌菌剂,以一株解磷巨大芽孢杆菌为研究对象,以OD600为依据测定活菌数量,优化最佳液体发酵培养条件。首先采用单因素试验对其培养条件如接种量、装液量、发酵温度、起始pH、发酵时间、摇床转速等进行筛选,获得单因素试验最佳值;在此基础上,利用L9(34)正交试验对其培养条件进行优化及验证,并制作菌株生长曲线。研究结果表明：该株巨大芽孢杆菌的最佳培养条件为：发酵温度30℃、起始pH 8.0、装液量20 mL/250 mL三角瓶、接种量3%、摇床转速250 r/min、培养时间22 h。在此最优条件下培养,以平板涂布法计数,发酵液最终活菌数达到3.2×109 cfu/mL以上。培养2~8 h,菌体生长处于对数期,8 h后菌体生长进入稳定期,22 h后进入衰亡期。试验结果为工业生产解磷巨大芽孢杆菌菌剂提供了基础数据。     

Dynamic analysis on ferromagnetic particles of magnetorheological fluids

Based on the theory of magnetic dipole, this paper analyzes the forces and moments applied on the particles and established the corresponding equations of motion. It compares these forces respectively in order to reduce the computation time in the numerical simulation. It is found that magnetic force, viscous force and repelling force are stronger than other forces, and translation is the main motion. Therefore the governing equation in the numerical simulation can be simplified. The validity of above dynamic analysis is verified by numerical simulation on the microstructure of magnetorheological fluids.