多孔介质中天然气水合物注热+降压开采的实验研究

为研究注热与降压相结合的开采方式是否更加有利于天然气水合物的开采,在自制的天然气水合物开采模拟实验系统上进行了实验研究.在一维填砂模型中人工生成天然气水合物之后,进行先注热盐水然后再降低压力(注热+降压)的开采模拟实验,分析了开采过程中系统温度、电阻率变化规律以及产气量、能量效率等.结果表明:产气规律具有明显的阶段性,...     

天然气水合物分解对地层稳定性影响的离心机实验模拟

水合物分解后将引起地层强度的降低,可能造成海床沉陷、滑塌以及海洋结构物基础的破坏。针对该问题,首先以南海浅层粉砂为沉积物骨架,采用生物厌氧发酵技术合成水合物沉积物,然后进行水合物热分解引起地层响应的离心机实验模拟,获得了水合物分解引起地层变形与滑塌的特征以及孔隙压力发展的物理过程,为研究水合物分解引起海床失稳的条件进行了新的尝试。     

具有越流的多层气藏的数值模拟研究

由于沉积的原因 ,油气藏通常由多层组成 ,每层的流体和岩石具有不同的物理性质。本文对打开全部气层进行合采的试井过程以及打开部分层进行合采的试井过程 ,利用有限差分方法编制了模拟试井程序。两层情形的数值解与解析解进行了比较 ,说明了数值方法的正确性。通过对模拟计算结果的分析 ,阐明了井底压力曲线的特点和利用该曲线进行试井解释的方法 ,并说明了气藏层间越流的特点及性状。     

The Effect of Asphalt Precipitation on Flow Behavior and Production of a Fractured Carbonate Oil Reservoir During Gas Injection

The first field data, collected over an 11 year period, are presented which indicate the possible effect of asphalt precipitation on the permeability and injectivity index of a fractured carbonate oil reservoir. The asphalt aggregates were formed during enhanced oil recovery by injection of a rich gas into the reservoir. The data indicate that, while at the initial stages of the operations the permeability and injectivity index decrease, at later times they appear to oscillate with the process time, with apparent oscillations' periods that depend on the heterogeneity of the reservoir. Two classes of plausible mechanisms that give rise to such oscillatory behavior are discussed. One relies on the changes in the structure of the reservoir's fractures, while the other one is based on asphalt precipitation in the reservoir. Computer simulations of flow and precipitation of asphalt aggregates in a pore network model of the reservoir are carried out. The results appear to support our proposition that asphalt formation and precipitation in the reservoir are the main mechanism for the observed behavior of the injectivity index. We also develop a stochastic continuum model that accurately predicts the time-dependence of the reservoir's permeability and injectivity index during the gas injection process.     

Experimental study on dynamics of an oblique-impact vibrating system of two degrees of freedom

The paper presents a detailed experimental study of an oblique-impact vibration system of two degrees of freedom. The primary objective of the study is to verify the hypothesis of instantaneous impact in the oblique-impact process of two elastic bodies such that the incremental impulse method works for computing the nonlinear dynamics of the oblique-impact vibrating systems. The experimental setup designed for the objective consists of a harmonically excited oscillator and a pendulum, which obliquely impacts the oscillator. In the study, the dynamic equation of the experimental setup was established first, and then the system dynamics was numerically simulated by virtue of the incremental impulse method. Afterwards, rich dynamic phenomena, such as the periodic vibro-impacts, chaotic vibro-impacts and typical bifurcations, were observed in a series of experiments. The comparison between the experimental results and the numerical simulations indicates that the incremental impulse method is reasonable and successful to describe the dynamics during an oblique-impact process of two elastic bodies. The study also shows the limitation of the hypothesis of instantaneous impact in an oblique-impact process. That is, the hypothesis only holds true in the case when the impact angle is not too large and the relative approaching velocity in the normal direction is not too low. Furthermore, the paper gives the analysis of the tangential rigid-body slip on the contact surface in the case of a large impact angle, and explains why there exist some discrepancies between the numerical simulations and the experimental results.     

输气管路弯头内壁面冲蚀进化的试验和数值模拟研究

砂粒的连续冲击使输气管路弯头内壁面连续不均匀地发生着冲蚀进化现象.本文作者基于3D成像技术精确描述了R/D=1.5弯头内壁冲蚀进化过程,并采用CFD方法对该过程进行了数值模拟研究.结果显示,随着颗粒冲击,磨损严重的区域向弯头圆心角高角度扩散的速度较大;通过修正Schiller Naumann拽力系数模型可较准确地模拟弯头的冲蚀进化过程(平均误差小于0.15 mm).以上工作对管路的完整性评价具有重要意义.     

Numerical study on the deformation of soil stratum and vertical wells with gas hydrate dissociation

Gas hydrate (GH) dissociates owing to thermal injection or pressure reduction from the well in gas/oil or GH exploitation. GH dissociation leads to, for exam-ple, decreases in soil strength, engineering failures such as wellbore instabilities, and marine landslides. The FLAC3D software was used to analyze the deformation of the soil stratum and vertical wells with GH dissociation. The effects of Young’s modulus, internal friction angle, cohesion of the GH layer after dissociation, and the thickness of the GH layer on the deformation of soils were studied. It is shown that the maximum displacement in the whole soil stratum occurs at the interface between the GH layer and the over-layer. The deformation of the soil stratum and wells increases with decreases in the modulus, internal friction angle, and cohesion after GH dissociation. The increase in thickness of the GH layer enlarges the deformation of the soil stratum and wells with GH dissociation. The hydrostatic pressure increases the settlement of the soil stratum, while constrain-ing horizontal displacement. The interaction between two wells becomes significant when the affected zone around each well exceeds half the length of the GH dissociation zone.     

3D Coupled Displacement Discontinuity and Finite Element Analysis of Reservoir Behavior during Production in Semi-infinite Domain

In this paper, we apply a DDM-FEM coupling method to reservoir simulation to evaluate the reservoir behavior over a compacting oil reservoir in half space. We use displacement discontinuity methods to account for the reservoir surroundings, and finite element methods in the fully coupled simulation of the reservoir itself.     

激波聚焦诱导点火和爆轰的数值研究

以二维轴对称多组分Euler方程为基础,采用非正交结构化网格和改进的波传播算法,模拟了激波在抛物形反射壁面聚焦反射诱导点火和爆轰的过程,描述了其流场形态。讨论了预混气组成、入射激波强度及反射壁面形状对点火和爆轰的影响。结果表明,激波在抛物形反射壁面顶点处聚焦反射可形成局部高温高压区域,该区域在一定条件下可点燃预混气甚至形成爆轰,其中低稀释剂浓度的预混气、较大的入射激波Mach数和较深的反射壁面有利于可燃预混气形成爆轰。     

一种超声速气动发电机实验装置及实验技术研究

在对超声速榴弹炮以及导弹引信供电系统的发电机研究中,过去常在闭口式风洞进行实验,但由于闭口式风洞中各种相似参数和特有的因素影响,使得实验数据与真实飞行数据完全不符。因此,多年来只得靠实弹打靶来完善设计方案。本文利用气体动力学和实验空气动力学理论,设计了一种适合气动发电机的超声速试验射流装置,并通过试验详细地研究了装置在出口的流场品质和不同几何外形气动发电机的转速特性,给出了合理的模型试验区、喷管出口流速的确定方法和射流实验区参考压力的选取方法,最后对模型实验结果与打靶遥测数据进行了对照。研究表明,利用超声速射流的工作原理进行导弹引信发电机的模拟实验是可行的,并且该装置可用于引信产品验收。     

Numerical and experimental study of a micro-blast wave generated by pulsed-laser beam focusing

This paper describes a numerical and experimental study of a micro-blast wave which is produced from the source of several tens microns in dia. and propagates in the length scale of a few centimeter in diameter. The micro-blast wave was generated by focusing a Nd:Glass pulsed-laser beam in ambient air. Its propagation and reflection were visualized by using double exposure holographic interferometry and simulated numerically using the dispersion-controlled scheme to solve the Euler and Navier-Stokes equations with initial conditions of a point-source explosion specified with the Taylor similarity law. Good agreement was obtained between numerical solutions and experimental results, and this spherical micro-blast wave was shown to be a handy model of blast waves created in large scale explosions. Received 28 October 1997 / Accepted 30 April 1998     

利用改进的ADI方法实现单机千万节点的油水两相渗流数值模拟

针对实际油藏的非均质分布特征及其复杂的边界条件,本文通过引入迭代参数的压缩因子和放大因子,对现有的交替方向迭代法(ADI)进行改进,提出一种适用于大规模油藏数值模拟的新算法．改进的ADI 方法计算精度可靠,且与现有的算法相比计算效率有所提高．更为关键的是,ADI 算法将求解三维压力方程的七对角矩阵分解为三个方向的三对角矩阵依次迭代求解,所需的运算存储量大幅减少,最大的计算规模有了大幅的提升．使用改进的ADI 方法,在单机上成功实现了千万节点的油水两相渗流数值模拟．计算实例表明,在同等单机硬件条件下,改进ADI 算法的最大计算规模是现有算法的1.7 倍以上．     

Experimental and Numerical Investigation on Cavitating Flows in Diesel Injection Systems

The present study is concerned with the phase change during rapid depressurization of fluids: the role of vapor bubbles nucleation and growth and the effect on the system fluid dynamics were modeled and experimental measurements were made. Following a control-volume approach, averaged equations governing the motion of a one-dimensional, homogeneous, no-slip two-phase flow were used considering both thermal equilibrium (equal temperature) and non-equilibrium (non-equal temperature) between the liquid and vapor phases. In the non-equilibrium model, the heat transfer from the liquid to the vapor and the corresponding mass transfer velocity were modeled. Model results were compared with experimental data for a loss-of-coolant accident in nuclear power plants: the comparison of numerical vs. experimental data showed the role of nucleation velocity during the earliest phase of rapid depressurization. The experimental study of two-phase flow in a diesel engine injection system has been carried out using a rotative pump which is operated by using a purpose-developed test-bench; pressure measurements inside the system pipes were performed using pressure transducers; moreover, an ultrasonic technique was employed to study phase change phenomena. Several measurements were performed comparing the results obtained by different experimental techniques with the model outputs.Sommario.presente studio riguarda il fenomeno della cavitazione durante la depressurizzazione di fluidi. E'stata considerata la velocità di formazione e nucleazione delle bolle di vapore e le equazioni di conservazione sono state integrate con solutori al 1°e 2°ordine di tipo ENO. Sono stati utilizzati dati sperimentali ottenuti durante incidenti per perdita di refrigerante in centrali nucleari; per quanto riguarda gli apparati di iniezione, gli autori hanno sviluppato due differenti tecniche sperimentali, basate rispettivamente sulla pressione e sulla riflessione degli ultrasuoni. Il confronto dei risultati numerici con quelli sperimentali è stato soddisfacente.     

Experimental and numerical study on a laminar fluid-structure interaction reference test case

With the rapid development of numerical codes for fluid-structure interaction computations, the demand for validation test cases increases. In this paper we present a comparison between numerical and experimental results for such a fluid-structure interaction reference test case. The investigated structural model consists of an aluminum front cylinder with an attached thin metal plate and a rear mass at the trailing edge. All the structure is free to rotate around the axle mounted in the center of the front cylinder. The model's geometry and mechanical properties are chosen in such a way as to attain a self-exciting periodical swiveling movement when exposed to a uniform laminar flow. Reproducibility of the coupled fluid-structure motion is the key criterion for the selection of the model in order to permit an accurate reconstruction of the results in the time-phase space. The Reynolds number of the tests varies up to 270 and within that range the structure undergoes large deformations and shows a strong nonlinear behavior. It also presents two different self-excitation mechanisms depending on the flow velocity. Hence, challenging tasks arise for both the numerical solution algorithm and the experimental measurements. To account for the two different excitation mechanisms observed on increasing the speed of the flow, results for two different velocities are considered: the first at 1.07 m/s (Re=140) and the second at 1.45 m/s (Re=195). The comparisons presented in this paper are carried out on the basis of the time trace of the front body angle, trailing edge coordinates, structure deformation and the time-phase resolved flow velocity field. They reveal very good agreement in some of the fluid-structure interaction modes whereas in others deficiencies are observed that need to be analyzed in more detail.     

Numerical simulation of blood flow and interstitial fluid pressure in solid tumor microcirculation based on tumor-induced angiogenesis

A coupled intravascular–transvascular–interstitial fluid flow model is developed to study the distributions of blood flow and interstitial fluid pressure in solid tumor microcirculation based on a tumor-induced microvascular network. This is generated from a 2D nine-point discrete mathematical model of tumor angiogenesis and contains two parent vessels. Blood flow through the microvascular network and interstitial fluid flow in tumor tissues are performed by the extended Poiseuille’s law and Darcy’s law, respectively, transvascular flow is described by Starling’s law; effects of the vascular permeability and the interstitial hydraulic conductivity are also considered. The simulation results predict the heterogeneous blood supply, interstitial hypertension and low convection on the inside of the tumor, which are consistent with physiological observed facts. These results may provide beneficial information for anti-angiogenesis treatment of tumor and further clinical research. The project supported by the National Natural Science Foundation of China (10372026).     

Experimental and numerical investigation on the flow field within a compact inlet duct

A combined experimental and numerical investigation of the flow field in a short, rectangular, diffusing S-shape inlet duct was conducted. The inlet duct had a length-to-hydraulic diameter ratio of 1.5 and an inflow Mach number of 0.44. The flow field was diagnosed utilizing stereoscopic particle image velocimetry, surface static pressure measurements, and high frequency total pressure measurements both on the lower surface and at the duct’s aerodynamic interface plane. To complement the experimental investigation and to aid in understanding the flow field associated with this complex geometry, a numerical flow simulation was undertaken. The flow field exhibited massive flow separations and shear layer formations at both turns of the compact inlet. Moreover, secondary flow structures along the duct’s lower surface and along the duct’s side walls were identified. It was shown that the two counter-rotating flow structures along the duct’s lower surface resulted in high levels of total pressure loss at the aerodynamic interface plane. A high fidelity spectral analysis of the pressure signals at the aerodynamic interface plane and along the lower surface was conducted and demonstrated that a high frequency surface static pressure sensor could identify flow separation in a non-intrusive fashion, allowing for future use in a closed-loop control scheme for active flow control. This work was part of a more comprehensive study which was to utilize active flow control to improve performance metrics of such compact inlets.     

Laboratory and Simulation Investigation of Enhanced Coalbed Methane Recovery by Gas Injection

Methane/carbon dioxide/nitrogen flow and adsorption behavior within coal is investigated simultaneously from a laboratory and simulation perspective. The samples are from a coalbed in the Powder River Basin, WY. They are characterized by methane, carbon dioxide, and nitrogen sorption isotherms, as well as porosity and permeability measurements. This coal adsorbs almost three times as much carbon dioxide as methane and exhibits significant hysteresis among pure-component adsorption and desorption isotherms that are characterized as Langmuir-like. Displacement experiments were conducted with pure nitrogen, pure carbon dioxide, and various mixtures. Recovery factors are greater than 94% of the OGIP. Most interestingly, the coal exhibited ability to separate nitrogen from carbon dioxide due to the preferential strong adsorption of carbon dioxide. Injection of a mixture rich in carbon dioxide gives slower initial recovery, increases breakthrough time, and decreases the volume of gas needed to sweep out the coalbed. Injection gas rich in nitrogen leads to relatively fast recovery of methane, earlier breakthrough, and a significant fraction of nitrogen in the produced gas at short times. A one-dimensional, two-phase (gas and solid) model was employed to rationalize and explain the experimental data and trends. Reproduction of binary behavior is characterized as excellent, whereas the dynamics of ternary systems are predicted with less accuracy. For these coals, the most sensitive simulation input were the multicomponent adsorption–desorption isotherms, including scanning loops. Additionally, the coal exhibited a two-porosity matrix that was incorporated numerically.     

Numerical simulation of soft palate movement and airflow in human upper airway by fluid-structure interaction method

In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient with Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS), three-dimensional models of upper airway cavity and soft palate are reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement of soft palate by fluid-structure interaction analysis. The reconstructed three-dimensional models precisely preserve the original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate. The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function of the upper airway as well as in diagnosing diseases related to anatomical structure and function of the upper airway. The project supported by the National Natural Science Foundation of China (10672036, 10472025 and 10421002), the Natural Science Foundation of Liaoning Province (20032109). English text was polished by Yunming Chen.     

间隔靶对射流侵彻影响的数值模拟和实验研究

对某聚能装药射流侵彻靶板的过程进行了数值模拟 ,得出其碰撞点附近应力分布与传统理论相符 ,侵彻深度与实验结果及工程计算结果基本相符 ;分别对该聚能装药侵彻连续靶和间隔靶的过程进行了数值模拟 ,数值模拟结果显示间隔靶的侵彻深度明显低于连续靶的侵彻深度 ,这说明侵彻开坑阶段的能耗侵深比远大于准定常阶段。为了验证间隔靶对射流侵彻的影响 ,用另一聚能装药分别对连续靶和间隔靶进行了侵彻实验 ,并排除了炸高的影响。实验结果也表明 ,间隔靶对射流侵彻的确存在着不利影响。还结合数值模拟及实验结果对传统的侵彻公式进行了修正。