Analysis of impact pressure,rock-breaking effect,and ground vibration induced by the disposable CO_(2)fracturing tube

The technology of expansion fracturing with liquid CO_(2)(EFLCO_(2))has attracted increasing attention due to reduced vibration and damage.The disposable fracturing tube has been developed and is gradually replacing the Cardox tube.However,there is a lack of impact pressure testing of disposable tubes under real working conditions,selection of gas explosion design parameters,and systematic analysis of blasting vibration.This limitation has constrained the widespread application of disposable fracturing tubes in engineering.A joint monitoring of the pressure-time curves in the disposable tubes and boreholes was conducted.The rock-breaking effect of varying hole spacing parameters in the EFLCO_(2)design was analyzed,and a systematic study was carried out on the vibration peak value,frequency,and energy characteristics.The results show that(1)the pressure distribution characteristics,stress peak value,and duration in the disposable tubes are different from those of Cardox tubes,which show multi-peak distribution,low-pressure peak value,and short duration.The correlation between the pressure in the disposable tube,filling pressure,and liquid CO_(2)weight is established,and a theoretical calculation method for the borehole wall pressure is proposed;(2)The hole spacing in rocks of different hardness is suggested;and(3)At the same scale distance,the peak particle velocity(PPV)caused by EFLCO_(2)(PPVCO_(2))is significantly smaller than that caused by blasting(PPVexplosive).The ratio of PPVexplosive to PPVCO_(2)is a power function related to scale distance,and a distance-related zonality exist in this relationship.The frequency composition of the vibration signal caused by EFLCO_(2)is relatively simple with a narrow frequency band.Its PPV and energy are mainly concentrated in the low-frequency band.This research contributes to the optimization of disposable fracturing tubes,gas explosion design,and vibration hazard control.

The effect of increased intra-abdominal pressure on orbital subarachnoid space width and intraocular pressure

In accordance with the trans-lamina cribrosa pressure difference theory, decreasing the trans-lamina cribrosa pressure difference can re- lieve glaucomatous optic neuropathy. Increased intracranial pressure can also reduce optic nerve damage in glaucoma patients, and a safe, effective and noninvasive way to achieve this is by increasing the intra-abdominal pressure. The purpose of this study was to observe the changes in orbital subarachnoid space width and intraocular pressure at elevated intra-abdominal pressure. An inflatable abdominal belt was tied to each of 15 healthy volunteers, aged 22-30 years （12 females and 3 males）, at the navel level, without applying pressure to the abdomen, before they laid in the magnetic resonance imaging machine. The baseline orbital subarachnoid space width around the optic nerve was measured by magnetic resonance imaging at 1, 3, 9, and 15 mm behind the globe. The abdominal belt was inflated to increase the pressure to 40 mmHg （1 mmHg = 0.133 kPa）, then the orbital subarachnoid space width was measured every 10 minutes for 2 hours. After removal of the pressure, the measurement was repeated 10 and 20 minutes later. In a separate trial, the intraocular pressure was measured for all the subjects at the same time points, before, during and after elevated intra-abdominal pressure. Results showed that the baseline mean orbital subarachnoid space width was 0.88 ＋ 0.1 mm （range： 0.77-1.05 mm）, 0.77 ＋ 0.11 mm （range： 0.60-0.94 mm）, 0.70 ＋ 0.08 mm （range： 0.62-0.80 ram）, and 0.68 _＋ 0.08 mm （range： 0.57-0.77 mm） at 1, 3, 9, and 15 mm behind the globe, respectively. During the elevated intra-abdominal pressure, the orbital subarachnoid space width increased from the baseline and dilation of the optic nerve sheath was significant at 1, 3 and 9 mm behind the globe. After decompression of the abdominal pressure, the orbital subarachnoid space width normalized and returned to the baseline value. There was no significant difference in the intraocular pressure before, during and after the intra-abdominal pressure elevation. These results verified that the increased intra-abdominal pressure widens the orbital subarachnoid space in this acute trial, but does not alter the intraocular pressure, indicating that intraocular pressure is not affected by rapid increased in- tra-abdominal pressure. This study was registered in the Chinese Clinical Trial Registry （registration number： ChiCTR-ONRC-14004947）.

Space-time analysis of the changing patterns of population pressure on the ecological environment in China

This paper examines the temporal change and spatial variation of population pressure on the ecological environment in China.We have collected sufficient data from the statistical yearbooks of 31 provincial administrative areas in 1990,1995,2000,2005,and 2010.Using a geographic information system(GIS) and relevant models,we analyzed the trend of the population pressure on ecological environment and the change of the gravity center of ecological environment quality.We conclude that:(1) generally,population pressure on the ecological environment in China was becoming higher during1990-2010,especially in some areas where the population and environment were in serious imbalance and the ecological environment experienced severe pollution;(2) during a certain period,population pressure on the ecological environment was becoming lower in some areas,but the ecological environment was getting worse;(3) the areas with super-high population pressure on the ecological environment were Beijing,Tianjin,and Shanghai;(4) the gravity center of population pressure on the ecological environment and the center of ecological environment quality move differently during the study time period,but the general trend was similar- both of them were moving from west to east.Based on the analysis,this paper also provides some policy suggestions on the control of ecological environment quality.

Pressure gradient errors in a covariant method of implementing theσ-coordinate:idealized experiments and geometric analysis

A new approach is proposed to use the covariant scalar equations of the a-coordinate （the covariant method）, in which the pressure gradient force （PGF） has only one term in each horizontal momentum equation, and the PGF errors are much reduced in the computational space. In addition, the validity of reducing the PGF errors by this covariant method in the computational and physical space over steep terrain is investigated. First, the authors implement a set of idealized experiments of increasing terrain slope to compare the PGF errors of the covariant method and those of the classic method in the computational space. The results demonstrate that the PGF errors of the covariant method are consistently much-reduced, compared to those of the classic method. More importantly, the steeper the terrain, the greater the reduction in the ratio of the PGF errors via the covariant method. Next, the authors use geometric analysis to further investigate the PGF errors in the physical space, and the results illustrates that the PGF of the covariant method equals that of the classic method in the physical space; namely, the covariant method based on the non-orthogonal a-coordinate cannot reduce the PGF errors in the physical space. However, an orthogonal method can reduce the PGF errors in the physical space. Finally, a set of idealized experiments are carried out to validate the results obtained by the geometric analysis. These results indicate that the covariant method may improve the simulation of variables relevant to pressure, in addition to pressure itself, near steep terrain.

Simulation study of the void space gas effect on slope instability triggered by an earthquake

This study aims at exploring the void space gas effect of earthquake-triggered slope instability and providing a new method for studying the formation mechanism of earthquake-triggered landslides. We analysed the basic characteristics, kinematic characteristics, initiation mechanisms and physical mechanical parameters of the Daguangbao landslide, generalized a landslide prototype, and established a geological model and performed simulation tests. Based on the seismic wave propagation theory of rock-soil mass, rock fracture mechanics and the effective stress principle, we found that the void space gas effect is due to the occurrence of excess void space gas pressure when the dynamic response of seismic loads impacts the void space gas in weak intercalated layers of the slope. The excess void space gas pressure generated by the vibration(earthquake) damages the rock mass around the void space with a certain regularity. The model test results show that the effective shear strength of the rock mass can be reduced by 4.4% to 21.6% due to the void space gas effect.

A Regularity Criterion Via the Pressure On the Three-dimensional Micropolar Fluid Equations in Besov Space

In this paper,we investigate the regularity criterion via the pressure of weak solutions to the micropolar fluid equations in three dimensions.We obtain that for 0<α<1 if p€L^(2/a)(0,T;B^α∞,∞),then the weak solution(u,ω)is regular on(0,T).

Experimental and simulation optimization analysis of the Whipple shields against shaped charge

Occasionally, the Whipple shields are used for the protection of a space station and a satellite against the meteoroids and orbital debris. In the Whipple shields each layer of the shield depletes part of high speed projectile en- ergy either by breaking the projectile or absorbing its energy. Similarly, this investigation uses the Whipple shields against the shaped charge to protect the light armour such as infantry fighting vehicles with a little modification in their design. The unsteady multiple interactions of shaped charge jet with the Whipple shield package against the steady homogeneous target is scrutinized to optimize the shield thickness. Sim- ulations indicate that the shield thickness of 0.75 mm offers an optimum configuration against the shaped charge. Exper- iments also support this evidence.

Effects of urban street trees on human thermal comfort and physiological indices: a case study in Changchun city, China

Planting trees along urban streets is one of the most important strategies to improve the urban thermal environment.However,the net impacts of urban street trees on human thermal comfort and physiological parameters are still less clear.On three similar east-west orientated streets with different degrees of tree cover-low(13%),medium(35%),and high(75%),urban microclimatic parameters and human physiological indices for six male students were simultaneously measured on three cloudless days in summer 2018.The results show that the differences in tree cover were predominant in influencing urban thermal environment and comfort.The street with the highest tree cover had significantly lower physiological equivalent temperature(PET) and more comfortable than the other two streets.The frequency of strong heat stress(PET> 35℃) was 64%,11 %,and 0%,respectively,for streets with low,medium,and high tree cover.For the six male university students,human physiological indices varied greatly across the three streets with different tree cover.Systolic blood pressure,diastolic blood pressure,and pulse rate increased with decreasing tree cover.The results also suggest that urban thermal environment and comfort had considerable impact on human physiological parameters.Our study provides reasons for urban planners to plant trees along streets to improve the thermal environment and promote urban sustainability.

Evaluation of Well Spacing for Primary Development of Fractured Horizontal Wells in Tight Sandstone Gas Reservoirs

Methods for horizontal well spacing calculation in tight gas reservoirs are still adversely affected by the complexity of related control factors,such as strong reservoir heterogeneity and seepage mechanisms.In this study,the stress sensitivity and threshold pressure gradient of various types of reservoirs are quantitatively evaluated through reservoir seepage experiments.On the basis of these experiments,a numerical simulation model(based on the special seepage mechanism)and an inverse dynamic reserve algorithm(with different equivalent drainage areas)were developed.The well spacing ranges of Classes I,II,and III wells in the Q gas field are determined to be 802–1,000,600–662,and 285–400 m,respectively,with their average ranges as 901,631,and 342.5 m,respectively.By considering both the pairs of parallel well groups and series well groups as examples,the reliability of the calculation results is verified.It is shown that the combination of the two models can reduce errors and provide accurate results.

Distribution of Stresses in Particulate Half Space under Surface Pressure

Reducing the linear system of two first order equilibrium equations involving normal stress σ(ρ,θ) and shearing stress v(ρ,θ), by elimination, to two decoupled second order equations in σ and v, we find that, for pressure only case, v(ρ,θ) vanishes in the half space. Consequently, the second order equation in σ can be simplified. In the language of linear system analysis, the medium(system) function, characterizing the mechanical behavior of a particulate medium in pressure only case, is obtained from the simplified second order equation ( 2 ρ+ 2 θ)σ(ρ,θ)=0 and can be inverted to give impulse reponse explicitly. Thus, response σ α(ρ,θ) may be computed directly from input, i.e., the surface pressure φ α(ρ) , by integration. Some explicit formulas for transmission problems, including response to input of strip linearly increasing pressure, are given in the paper.

A Novel Staggered Semi-implicit Space-Time Discontinuous Galerkin Method for the Incompressible Navier-Stokes Equations

A new high-order accurate staggered semi-implicit space-time discontinuous Galerkin(DG)method is presented for the simulation of viscous incompressible flows on unstructured triangular grids in two space dimensions.The staggered DG scheme defines the discrete pressure on the primal triangular mesh,while the discrete velocity is defined on a staggered edge-based dual quadrilateral mesh.In this paper,a new pair of equal-order-interpolation velocity-pressure finite elements is proposed.On the primary triangular mesh(the pressure elements),the basis functions are piecewise polynomials of degree N and are allowed to jump on the boundaries of each triangle.On the dual mesh instead(the velocity elements),the basis functions consist in the union of piecewise polynomials of degree N on the two subtriangles that compose each quadrilateral and are allowed to jump only on the dual element boundaries,while they are continuous inside.In other words,the basis functions on the dual mesh arc built by continuous finite elements on the subtriangles.This choice allows the construction of an efficient,quadrature-free and memory saving algorithm.In our coupled space-time pressure correction formulation for the incompressible Navier-Stokes equations,the arbitrary high order of accuracy in time is achieved through tire use of time-dependent test and basis functions,in combination with simple and efficient Picard iterations.Several numerical tests on classical benchmarks confirm that the proposed method outperforms existing staggered semi-implicit space-time DG schemes,not only from a computer memory point of view,but also concerning the computational time.

New method of predicting surge pressure apply to horizontal well based on casson flow

In order to predict the surge pressure caused in the horizontal well drilling process, a new simple and applicable method has been established. It is based on the general theory of hydrostatic drilling fluid mechanics, and specifically described the flowing physical model towards surge pressure in horizontal well annulus, taking the effect of string eccentricity on the flowing law of drilling fluid into consideration. According to the constitutive equation of casson-mode under one-dimensional steady flow and the equations of annular flow rate under different drill string working conditions, this paper introduced the flow rate computation models of axial laminar flow in eccentric annulus apply to horizontal well, of which the numerical model was calculated by the program called Mathematica, ultimately, a new model for surge pressure prediction towards each interval in horizontal well was put forward. Application examples indicated that it can solve questions easily and precisely, which presents important meaning of guidance to the safety control while horizontal well drilling.

Diffraction of plane P waves by a canyon of arbitrary shape in poroelastic half-space (Ⅱ): Numerical results and discussion

This paper investigates in detail the nature of diffraction of plane P waves around a canyon in poroelastic half-space, and studies the effects of incident frequency, drainage condition, porosity, etc, on the diffraction of waves. It is shown that the surface displacement amplitudes of the drained case are close to those of the undrained case, however, the surface displacement amplitudes of the dry case are very different from those of the saturated （either drained or undrained） cases. There are large phase shift between the dry case and the saturated cases, as well as slightly longer resultant wavelengths for the undrained case than those for the drained case and longer resultant wavelengths for the drained case than those for the dry case. For small porosity the surface displacement amplitudes for the saturated cases are almost identical to those for the dry case; while for large porosity, the effect of drainage condition becomes significant, and the surface displacement amplitudes for the undrained case are larger than those for the drained case. As the incident frequency increases, the effect of porosity becomes significant, and more significant for the undrained case than that for the drained case. As the porosity increases, the pore pressures increase significantly but their oscillations become smoother. As the incident frequency increases, the pore pressures become more complicated.

Analytical solutions for dynamic pressures of coupling fluid-solid-porous medium due to P wave incidence

Wave reflection and refraction in layered media is a topic closely related to seismology,acoustics,geophysics and earthquake engineering.Analytical solutions for wave reflection and refraction coefficients in multi-layered media subjected to P wave incidence from the elastic half-space are derived in terms of displacement potentials.The system is composed of ideal fluid,porous medium,and underlying elastic solid.By numerical examples,the effects of porous medium and the incident wave angle on the dynamic pressures of ideal fluid are analyzed.The results show that the existence of the porous medium,especially in the partially saturated case,may significantly affect the dynamic pressures of the overlying fluid.

Diffraction of plane SV waves by a cavity in poroelastic half-space

This paper presents an indirect boundary integration equation method for diffraction of plane SV waves by a 2-D cavity in a poroelastic half-space.The Green＇s functions of compressive and shear wave sources are derived based on Biot＇s theory. The scattered waves are constructed using fictitious wave sources close to the boundary of the cavity, and their magnitudes are determined by the boundary conditions. Verification of the accuracy is performed by： （1） checking the satisfaction extent of the boundary conditions, （2） comparing the degenerated solutions of a single-phased case with well- known solutions, and （3） examining the numerical stability of the solutions. The nature of diffraction of plane SV waves around a cavity in a poroelastic half-space is investigated by numerical examples.

Study of generation characteristics of glow-type atmospheric-pressure plasma jet based on DC discharge in air

In order to form an atmospheric-pressure plasma jet without airflow, a needle–ring electrode structure is proposed in this paper. When heteropolar potentials are applied to a needle and a ring, a marked electric field strength enhancement around the needle’s pointed end has been found. When the same potential is applied to both the needle and the ring, the lateral electric field strength for the needle can be weakened. By using the above two methods, an increase of the difference between the pointed end electric field strength and the lateral one is achieved and stable plasma jets are formed. A symmetrical space electric field distribution is established at the pointed end of the needles when several sets of heteropolar needle–ring electrodes are uniformly arranged, which is conducive to forming a uniform array plasma jet. Under DC discharge conditions, a safe and stable plasma jet of high density and an array plasma jet are successfully achieved.

Flow resistance characteristics of water in narrow annulus during heat exchange

Considering the special resistance characteristics of fluids flowing through ducts with small gaps, experiments are performed to investigate the resistance characteristics of single-phase water, which is forced to flow through ver tical annuli. The gap sizes are 0.9, 1.4 and 2.4mm, respectively. The experiments are conducted under condition of 1atm. The water in the annuli is heated by high temperature water reversely flowing through the inner tube and the outer annulus. The results show that the flow pattern begin to change from laminar to turbulent before Reynolds number approaches 2000, the flow resistance in annulus has little relations with the temperature difference and ways of being heated, but mainly depends on the ratio of mass flux to the width of annulus.

基于随机森林和长短期记忆网络模型的高压气井环空带压预测方法

高压气井在生产过程中持续的环空带压容易引起套管柱变形或挤毁,是高压气井完整性失效的主要原因之一。为解决传统方法环空带压预测精度不高的问题,以鄂尔多斯盆地苏里格气田某高压气井为例,首先利用主成分分析法和相关系数法找到影响环空带压的主要因素,然后使用高压气井井筒温压场理论值和孤立森林模型对主成分进行物理解释和数据清洗,再对清洗后的数据使用随机森林(RF)和长短期记忆网络(LSTM)模型建立了环空带压定量预测模型,并对两类模型进行权重组合,最终建立了精确度高于任意单一模型的RF—LSTM组合环空带压预测新模型。研究结果表明:(1)环空带压的主要影响因子有温度分量、压力分量、产量分量、腐蚀程度、生产状态,而温度分量与环空带压间存在最高关联性;(2)通过错误格式、离群点及基于井筒温压场的数据清洗,可以得到数据清洗后的环空带压影响因素训练集;(3)通过平均绝对误差法(MAE)能够建立误差分数小于任意单一模型,而拟合优度介于两者之间的组合模型,因此可以将具有高拟合优度和低误差分数的两类模型结合,从而组合出同时满足两种分数的组合模型。结论认为:(1)运用大数据挖掘技术及算法进行环空带压定量预测,方法新颖,预测精度高,结果可行;(2)该方法为现场环空带压预测和风险管控提供了决策工具参考,为实现环空带压风险实时预测、预警和管控提供了理论支撑。

PRESSURE DISTRIBUTION ON THE WALL OF THE INNER CYLINDER RECIPROCATING AXIALLY TO THE UNSTEADY FLOW OF VISCOELASTIC FLUID IN ECCENTRIC ANNULUS

In this article, the governing equations for the unsteady flow of viscoelastic fluid in the eccentric annulus with the inner cylinder reciprocating axially and the expression of the pressure distribution on the wall of the inner cylinder of the annulus are established and derived, respectively, under the bipolar coordinate system. The equations and the expression are solved and calculated numerically using the finite difference method, respectively. The curves of the pressure distribution on the wall of the inner cylinder of the aqueous solution of Hydrolyzed Polyacrylamide （HPAM） are plotted and the influences of annular eccentricity, stroke, and stroke frequency on the pressure distribution are analyzed.

油雾爆燃机理实验平台的搭建与教学实验设计

为了探究受限空间内油雾爆燃事故机理及事故后果,设计了可视化的油雾爆燃机理测试实验平台。通过“实验平台功能需求分析-平台设计与开发-实验设计与实施-数据采集-结果分析”全过程,实现实验平台开发与各种船舶舱室、石油炼化生产过程及其他工业生产中油雾爆燃事故模拟实验。通过爆燃火焰传播规律、舱室内温度场、压力场的测试与分析,揭示了油雾爆燃发展规律。爆燃峰值压力可达0.9 MPa。爆燃温度较高,舱内峰值温度达到988℃,油雾爆燃破坏性较强。该实验增强了教学过程的直观性、交互性和多感知性,提高了学生的安全意识和解决复杂工程问题的探究能力,培养了学生的实践创新能力,提升了实践教学的质量。