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孤岛微电网因线路阻抗各异，采用传统下垂控制无法实现功率按分布式电源容量比例分配，会产生电压/频率偏差。为此，提出一种基于DE-RBF混合优化算法的自适应下垂控制策略。首先，构建下垂控制的两逆变器并联微电网系统动态模型，应用差分进化 （differential evolution，DE） 算法获得多个平衡点的优化下垂控制参数。为提高系统的动态响应速度与稳定性，通过训练径向基 （radial basis function，RBF） 神经网络，对每个平衡点参数进行校正。进而，通过增加RBF神经网络的隐含层数量，推广至多个逆变器并联微电网。以采集的有功功率和无功功率作为训练数据，输出最优下垂系数，实现微电网的自适应下垂控制。最后，搭建Matlab/Simulink仿真平台，验证了所提自适应下垂控制方法相比于传统下垂控制，系统响应速度快，功率按照分布式电源容量比例分配。

畜禽副伤寒为常见病,而野生动物副伤寒较少见,笔者在检验工作中遇到貉副伤寒沙门氏菌病一例,特将其病理形态学观察结果报道如下: 1987年9月本省自治县某镇个体养貉户中流行一种疾病,患貉多为5月龄左右的仔貉,其临床症状为拒食,精神沉郁、鼻镜发绀,体温升高,脓性眼眦,粪便呈粥样或水样,常混有大量粘液,口吐

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Assisted drilling with non-liquid technologies,such as supercritical CO2 jet, are more and more important in natural gas exploration, especially in coal-bed methane exploration. As a kind of non-liquid technologies, abrasive gas jet is widely used to drill metal and glass. It is also powerful enough to break coal and rock, which is the primary precondition of its usage in coal-bed methane exploration.To understand the rock erosion wear mechanism of abrasive gas jet is critical important to apply the technology preferably and widely. However, the existing erosion mechanism mostly neglects the effect of rebound abrasive. To this end, the experiments of limestone erosion by the abrasive gas jet under different kinds of abrasives and different stand-off distances were carried out. The experiment results show that the ero-sion pit has an approximate inverted cone-shape. The bottom of erosion pit is of hemispherical. There is an annular platform above the hemispherical bottom, which connects the bottom and side of erosion pit. The primary reason that induces the peculiar shape of erosion pit is the specific flow field of abrasive gas jet. There is an annular region between the axis and boundary of the abrasive gas jet, and there is no abrasive in the annular region. The abrasive around the axis induces the formation of hemispherical bottom. After rebounding, the abrasive around axis moves to the annular region. The rebound abrasive with high velocity enlarges both the diameters of hemispherical bottom and erosion pit and induces the formation of annular platform. The failure characteristics of different areas of the erosion pit were analyzed by Scanning Electron Microscopy(SEM). It can be concluded that the failure models of different spots are different. The failure is caused by the impact stress wave of the incident abrasive at the base of the hemispherical bottom. Plastic deformation is the primary failure model induced by the rebound abrasive at the side of hemispherical bottom. The plastic deformation induced by incident abrasive and fatigue failure induced by rebound abrasive are the primary failure model at the annular platform. Fatigue failure induced by rebound abrasive is the primary model failure at the side of erosion pit. The rock failure reason of abrasive with different hardness is the same, but the rock damaged by hard abrasive has rougher surface and higher rock breakage efficiency. [ABSTRACT FROM AUTHOR]

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With the changes of gas pressure during the gas drainage process, the dynamic evolution of seam permeability occurs. The dynamic evolution of coal permeability was the result of interaction of matrix contraction and effective stress.In the paper, the change relationship of coal seam permeability during the gas desorption, diffusion and percolation process was theoretically deduced based on the fractured plate model. A dynamic evolution model on permeability was established based on surface chemistry theory and effective stress principle. The model was validated according to the measured parameters in coal mines. The results show that the relationship between permeability and gas pressure is asymmetric U-shaped variation law. It closely matches the experimental results in the laboratory. Therefore, the correctness of this model is verified. [ABSTRACT FROM AUTHOR]

To investigate the mechanism for the photocatalytic degradation of coal-mine gas over self-made adsorptiontype composite catalyst（ 15% Ga2O3/AC）, the experiments of photo-assisted removing methane in simulated coal-mine gas are carried out. The compound effect, interfacial microstructure, pore volume, pore size distribution and specific surface area of composite catalysts are characterized by X-ray diffraction（ XRD）, high-resolution transmission electron microscopy（ HRTEM） and low temperature N2 adsorption-desorption technique, respectively. The separation of photo-induced charge carriers, the transfer of photo-generated electrons and the generation of reactive species are studied by using photoluminescence spectrum（ PLs） and electron spin resonance（ ESR） spectra. Based on the analysis of methane degradation kinetics, the effective photo-assisted degradation of low concentration coal-mine gas can be implemented repeatedly, keeping almost unchanged removal efficiency. The introduction of coal-based AC can enhance the adsorption of methane, meanwhile improve the separation of photo-generated charge carriers, which contributes to producing more photo-hole（ h+） and superoxide radical( O2·-). The generated ·CH3 via CH4 hydrogen abstraction by h+is further oxidized through the reaction with O2·-, promoting the removal efficiency of methane. These results provide a theoretical basis for the gas control in the local region of coal mine using photo-oxidation technology. [ABSTRACT FROM AUTHOR]

In order to reveal the water outburst mechanism of Karst collapse pillars (KCP) and provide theoretical basis for the water outburst prevention, based on the dual-porosity media seepage theory, the authors consider KCPs as three main components, i. e. solid matrix, fluid and filling material in fractures between matrix, then a mechanical model for KCP water outburst involving the processes of solid deformation, water flow, particles erosion and migration, fracture and the permeability change were presented. The seepage characteristics of KCPs were investigated by numerical simulation based on engineering practice, obtaining the variation of porosity, seepage velocity, water pressure, particles concentration as well as water inflow volume as the time. The research results indicate that ① the water inflow of KCP obtained by numerical simulation is agreed with the field test data, which indicates the correctness of the mechanical model. ② the particles in KCPs will be eroded and transported under the coupling effect of deformation-seepage-erosion, fractures will increase rapidly, then several main seepage channels will form and eventually cause the KCP water outburst accident. [ABSTRACT FROM AUTHOR]

Using Split Hopkinson Pressure Bar (SHPB) experimental system, the experiments on the failure characteristics of coal samples taken from Weiding coal mine under impact loading were carried out. Then the coal dynamic mechanical properties were analyzed in detail. According to the experimental data, it is clear that coal is a typical rate-depended material. Moreover, both the coal elastic modulus and compressive strength increase with the strain rate increases. Besides, a strength statistical damage constitutive model of coal was built based on the strength theory and statistical damage theory, a method to determine the model parameters was proposed,and the model correctness was verified by the testing data.The model is proved to be accurate and reasonable compared with the component statistical damage constitutive model. The research results show that the strength statistical damage constitutive model not only can effectively describe the coal dynamic mechanical properties, but also has several advantages, such as simple construction, few parameters and clear physics meaning. Therefore, the model with high relevance is more suitable and universal to describe the coal dynamic mechanical properties than the component statistical damage constitutive model. [ABSTRACT FROM AUTHOR]

The phenomenon of blocking hole and drill holding often occurs when using water jet cutting,and hydraulic punching to enhance the gas drainage in soft coal seams. To solve such problems, a device and an integrated method for breaking coal, dredging and slagging are developed in this paper. Through controlling the direction of water with water pressure, the high pressure water is used to break coal and relief pressure or dredge slag. Based on the analysis of the causes of plugging holes, according to the continuous medium model, the force of the drill pipe was analyzed and the mechanics mechanism of holding and drilling were investigated. The relationship between the torque of drilling rig and the length of the hole and the parameters of the hole is obtained. Based on the analysis of the water jet drilling, the critical parameters of jet dredging slag were studied, and the critical nozzle installation position of dredging was obtained. In addition, a coal breaking, dredging and discharging device and its integration process were developed. Accoiding to the field test,the new method can effectively eliminate the hydraulic pressure relief in the process of the emergence of plugging hole,and holding drill. [ABSTRACT FROM AUTHOR]

In terms of the shortcomings of hole collapse and the suppression of gas desorption and migration caused by using hydraulic anti-reflection measures in soft and low permeable coal seam，this paper put forward a technical method of using high pressure gas jet to break coal，relieve pressure and anti-reflection. According to thermodynamics correlation theory，the critical local velocity and pressure of stress wave caused by gas jet breaking coal were calculated and analyzed and the high pressure gas jet breaking coal experiment was carried out. When high pressure gas jet impacted coal body，the quasi-static load and dynamic load acted on it and caused the coal body surface to form some erosion pits. In the way of stress wave，the coal body could be cut through by cracks loading which resulted in rupture. By establishing the dispersion equation of stress wave propagation in coal body，the influence of porosity and permeability on stress wave propagation in coal was analyzed. The result shows that the porosity has a significant effect on the wave velocity. With the increase of the porosity，the attenuation of stress wave shows an obvious tendency，and the attenuation of stress wave becomes more obvious in high frequency. At a low frequency，the permeability has little influence on the wave velocity. At a high frequency，the wave velocity increases with the increase of permeability when the permeability is low. In addition，the wave velocity attenuation shows a tendency of increasing first and decreasing later. When the permeability is greater than 10-11，the wave velocity is not affected by the permeability，and the stress wave is not attenuated. [ABSTRACT FROM AUTHOR]

A tri-axial creep-seepage-adsorption and desorption experimental device has been developed to study seepage law and gas adsorption and desorption characteristics in the process of loaded gas bearing coal rheology. It is composed of testing main machine, servo-controlled loading system, triaxial compression chamber, pore pressure control system, adsorption and desorption system, temperature control system, deformation monitoring system and safe guard system. The maximum axial pressure is 500 kN, and the maximum confining pressure is 50 MPa. The heating temperature can reach as high as 90 ℃; and the dimensions of tested cylinder samples are φ50 mm×100 mm. The advantages of the device are as follows:① It can be used to test the porosity and mechanical parameters of coal and to carry out the gas adsorption desorption and creep-seepage experiments of loaded gas-bearing coal and other experiments as well. The device,in addition, is powerful in function, stable in performance and accurate in testing.② It can also be fitted to conduct creep-seepage experiments for long time because of adopting the ball screw loading mode. And the maximum loading time can be more than two months.③ The device is equiped with high and low temperature control system. And it can be used to keep the constant temperature at the gas inlet, gas outlet and the triaxial compression chamber, which can effectively avoid the messurement error caused by temperature variation. Experiments of coal porosity testing, gas desorption characteristics and creep-seepage law of loaded coal are conducted using this device. These conclusions validate the functional diversity, accuracy and reliability in testing on the device. [ABSTRACT FROM AUTHOR]

In order to study the change of microstructure of coal under temperature impact, the temperature impact experiment of coal was carried out by using high and low temperature test system. Scanning electron microscopy (SEM) , industrial micro-CT, mercury injection experiments and cryogenic liquid nitrogen adsorption experiments were used to characterize the evolution of the pore fracture structure of coal before and after temperature shock. Based on digital image processing technology, the SEM images of coal reservoirs were binarized before and after temperature impact, and the fissure width variation of coal reservoirs was qualitatively and quantitatively analyzed. Also the specific surface area and pore size of pores in coal reservoirs were statistically analyzed before and after temperature shock. The results show that the temperature impact causes the large pores in the coal sample to penetrate each other and form macroscopic cracks, resulting in a corresponding decrease in the volume of macropores and an increase in the volume of mesoporesand small pores. The maximum thermal stress generated during the temperature impact test is located in the tangential direction of the surface of the coal sample. The thermal stress generated by the temperature shock exceeds the tensile strength of the coal sample, which is the direct cause of crack initiation, expansion and mutual penetration. The research results can provide technical support for the efficient development of coalbed methane and the improvement of gas drainage rate in coal seams. [ABSTRACT FROM AUTHOR]

In order to study the characteristics of anisotropic seepage of coal bearing methane, the raw coal samples were taken. Based on the tri-axial seepage experimental system the study of anisotropic seepage rule of coal hearing methane was carried out. The calculation method of the principal value and its azimuth of anisotropic permeability of coal bearing methane were determined. Permeability anisotropic ratio of coal bearing methane was defined. Permeability anisotropic dynamic variation rule and the phenomenon of the change of the dominant flow direction of coal bearing methane were analyzed emphatically. The results show that the flow of methane of coal has the very obvious characteristics of anisotropy, the calculation method of anisotropy permeability of coal bearing methane proposed in this paper is simple and effective. The coal bearing methane has strong stress-sensitivity, and the variation rule between permeability of methane of coal and effective stress is according with negative exponential function. The change of the permeability anisotropy of methane of coal with effective stress shows an obvious dynamic change law of development, the dominant flow direction of methane of coal exists the phenomenon of change. [ABSTRACT FROM AUTHOR]

In order to meet the requirements of low-carbon economy,the reduction and utilization of global-warming gases have become the focus of attention.There are a large amount of toxic and harmful gases being emitted from the combustion of fossil fuels and syngas,as well as being released during mining activities.It is therefore necessary to trap and separate these gases for eliminating their environmental contamination,also increasing the feedstocks for industrial production.For avoiding the contamination and safety problems raised from the conventional alkali absorbents,the ionic liquids,namely “liquid molecular sieve”,have become green alternatives to absorb and separate different gases.Accordingly,the research progress about separating gases by pure ionic liquids is reviewed in this paper.The influencing factors including temperature,pressure,the properties of gas and ionic liquids,and the functional groups of ionic liquids,were analyzed.It is stated that the ionic liquids with alkali groups on cation and anion are promising CO2solvents and competent separator for removing CO2from some sparsely soluble gases.In order to separate CO2from strongly acidic SO2 and H2S,moderate basicity exhibits much better separating ability because strong alkali group could strongly bind with both SO2(or H2S) and CO2,leading to low SO2/CO2and H2S/CO2 selectivities.Ionic liquids with small molecular weights and compact structures usually perform better selectivity,and low temperature and pressure are favorable for increasing the separation.Additionally,combining experimental results and molecular dynamic simulation,the real selectivity of binary gases in ionic liquids was calculated based on Equations of State.It is concluded that feed gas ratio,ionic liquid contents,temperature and pressure are significant factors required to be adjusted to approach a great real gas selectivity. [ABSTRACT FROM AUTHOR]

If the criterion of rock breakage with high pressure water jets is developed based on stress-strain,the precision of the criterion depends on the function type of yield stress.And the precision is not high enough for rock breakage with high pressure water jets,because of being lack of critical rock parameters.But if the criterion is developed based on energy,its precision will be high enough and its applicability will be general.The paper studied the mechanism of rock breakage with high pressure water based on energy dissipation and release.The kinetic energy of potential core area and boundary layer was calculated based on the velocity distribution of free jet,and then the kinetic energy calculation model of high pressure water jets was developed.The rock breakage energy of high pressure water jets represented the formation of erosion pit and volumetric fracture of rock.Part of energy dissipated fracture propagation and slip plane.And part of energy reserved as elastic potential energy in rock,which leaded to the volumetric fracture of rock.According to the unified energy yield criterion of rock,the energy criterion of rock breakage with high pressure water jet was developed.The primary rock parameters of sandstone,limestone and granite were tested by uniaxial compression experiment.Then the shear strain energy and volumetric energy of three type rocks can be calculated respectively.So,the critical speed of high pressure water jets can be figured out.According to the experimental results of rock breakage,the energy criterion of rock breakage with high pressure water jet was amendment,combining with the discharge coefficient of nozzle.The amended criterion was more precise for coal breakage with high pressure water jets.And the failure mode of rock proved that the energy criterion was more suitable for the mechanism of coal breakage with high pressure water jets. [ABSTRACT FROM AUTHOR]

To study the change law of permeability of coal under the condition of temperature impact and the mechanism of increasing permeability，the temperature impact test of two kinds of conditions of coal samples were carried out using thermostat and liquid nitrogen，the permeability variation of coal samples before and after temperature shock and the development of micro fracture were analyzed，and the distribution of acoustic emission signal in the process of temperature shock was also discussed.The experimental results indicate that after the cold shock treatment and hot-cold shock treatment，an average increase of permeability of coal were 48.68% and 469.24% respectively，the AE energy peak during hot-cold impact process is 3.6 times of that during the cold shock process.Compared with cold shock treatment，the hot-cold impact process produces more number of crack，the fractures show a dendritic development，and the effect of increasing permeability is better.The thermal stress exceeding the tensile strength of coal produced by the anisotropy and thermal shock properties of coal is the main mechanism of increasing permeability. [ABSTRACT FROM AUTHOR]