渠道水力计算表及其原理

大家知道,各种用途的各类渠道都要进行渠道设计.在渠道的横断面设计中,必须进行渠道的水力计算.渠道水力计算的主要任务是计算渠道的断面尺寸,以保证能通过所要求的流量,或校核已建成的渠道是否具有所要求的输水能力. 梯形渠道水力计算通常采用试算法,由于试算没有定量的规律可循,所以计算往往较繁.特别是在缺乏实践经验的情况下可能会作一些不必要的试算.     

混输管道数据库压降插值计算方法研究

在计算压降的经验公式与理论公式的基础上,提出了基于混输管道数据库水力插值计算方法,采用SQLServer2008与visualC.NET软件建立油气水混输管道数据库并开发数据库管理平台,实现水力插值计算,以环道试验数据作为基础数据对插值预测法计算结果进行验证,并与PIPEPHASE软件及OLGA软件计算结果进行对比分析,结果表明:插值预测法计算误差在PIPEPHASE软件及OLGA软件最小误差基础上降低30%以上.     

渠道水力最优断面设计算图的一种编制方法

在进行渠道水力计算的过程中,当流量 Q、渠道底坡 i 及糙率 n 已知的情况下,都希望得到最小的过水断面面积,以减少土石方开挖量,或者说,在过水断面面积、渠底坡度和糙率一定的条件下,使渠道所通过的流量最大.水力学中把满足上述条件的断面形式叫做水力最优断面.     

数学公式在水力计算中的应用

从理论上阐述了将数学中的牛顿法公式应用于复杂水力计算问题的可行性 ,并通过算例进行实际运算 ,对解决实际工程计算问题具有指导意义 .     

基于扩展有限元的页岩水力压裂数值模拟

考虑裂缝内流体流动和周围岩石应力变形,建立了页岩人工裂缝扩展的数学模型,分别采用有限元和扩展有限元求解裂缝流场和岩石应力场,并通过Picard迭代方法耦合求解,计算结果与经典模型结果吻合,验证了模型正确性.在此基础上,分析了岩石弹性模量、Poisson(泊松)比和注入速度对裂缝几何形态的影响以及水力裂缝任意角度逼近天然裂缝扩展动态.结果表明:弹性模量和注入速度对裂缝形态具有重要影响,而Poisson比对裂缝形态影响较小;随着页岩脆性增高,压裂裂缝趋于"长窄型"扩展;地应力差和逼近角越大,水力裂缝越易贯穿天然裂缝;水力裂缝与天然裂缝相交处裂缝宽度存在相对较大的降低;扩展有限元方法避免了计算过程中的网格重构与网格加密,减少了计算量,该模型可以为页岩压裂设计提供理论指导.     

复杂水力计算中的高次方程问题

将实际工程中的复杂水力计算问题归纳为对高次方程的求解,并提出快速、正确解决这类问题的数值方法——中点迭代法,对解决实际工程问题具有指导意义.     

梯形复式断面均匀流水力计算

对由主槽、斜边坡以及边滩三部分组成的梯形复式断面渠道均匀流的水力计算进行了研究,采用表观切应力表示各子断面间的横向动量交换,结合各部分力的平衡关系式,推导出了主槽、斜边坡和边滩平均流速的计算公式．采用UK-FCF的实验数据对公式进行了验证,滩槽相对水深为0.057~0.4的7组工况计算值与实测值的比较表明,不考虑表观切应力的计算值与实测值的一致性都较差．比较而言,斜边坡部分平均流速在水深较小时计算值大于实测值,在水深较大时计算值小于或接近实测值,表观切应力对边滩部分平均流速的影响不明显,而主槽部分若不考虑表观切应力的影响,则计算值与实测值差别较大．运用三段式模型与刘沛清等提出的两段式模型分别进行了有边坡梯形断面复式渠道的水力计算,结果表明对于有边坡段的梯形断面渠道（河道）,三段式模型更加有效．最后,将计算的表观切应力与实测表观切应力进行了比较,两者的一致性表明采用的动量输运系数是合适的．     

基于数值模拟方法的水力压裂分支裂缝产能预测研究

水力压裂是开发低孔、低渗/特低渗油气储层无可替代的技术.而在重复压裂、转向压裂和体积压裂中均可能产生分支裂缝,对于水力压裂后形成分支裂缝的储层进行产能预测是非常必要的一项工作.建立了数学模型对具有分支裂缝系统的储层进行了产能模拟.首先,通过定量化描述裂缝的起点位置、角度和长度,实现了裂缝系统的描述.其次,采用二维单相可压缩液体不稳定渗流,将带有分支裂缝的储层视为各向异性的非均质储层,建立了数学模型.并根据数学模型,采用中心差分法建立差分方程组,给出了计算步骤和流程.最后,对实际的一口井进行了拟合并进行了敏感性参数分析,效果较好.数学模型和方法可作为分支裂缝产量预测的有效工具.     

垂直裂缝气井生产动态预测及参数识别

为了摆脱分析解释水力压裂裂缝参数时选择图版的繁复工作和克服人为的误差,在引入非达西因子的基础上,考虑裂缝导流能力在生产过程中的变化,提出了垂直裂缝气井中真实气体在地层-裂缝系统中非达西渗流的数学模型和生产动态预测模型,建立了识别垂直裂缝气井水力裂缝参数的生产历史自动拟合模型,并给出了数值解法,为认识和了解气层、分析和评估气井压裂施工质量,提供了准确可靠的方法。     

考虑流固耦合效应的重力坝水力劈裂模拟

裂缝的高压水力劈裂是混凝土高坝安全评估的重要部分,研究其过程中的流固耦合作用是准确预测在各种情况下裂纹扩展路径和危险程度的关键.该文利用扩展有限元法在模拟裂纹扩展方面的优势,对大坝的裂纹进行水力劈裂模拟研究.裂纹中的水压分布模型采用Brühwiler和Saouma水力劈裂试验的成果,体现了水压和裂纹宽度的耦合关系,给出了扩展有限元在裂纹面上施加水压力荷载的实施方法,对一典型重力坝裂纹的水力劈裂进行了数值模拟分析.研究结果表明:采用扩展有限元法模拟水力劈裂,克服了常规有限元法存在的缺点,裂纹扩展时不用重新划分网格,裂纹的实时宽度可以由加强节点的附加自由度得到,裂纹面上水压的施加也变得简单易行.当考虑裂纹内的流固耦合效应时,裂纹的扩展路径相比不考虑耦合效应时的扩展路径(均布全水头水压),扩展角变大,扩展距离变短.     

应用模糊综合评判方法优选水力压裂井

考虑到水力压裂井压裂效果影响因素之间的关系复杂,且各影响因素本身具有模糊性,这些因素很难用常规方法量化研究,尝试应用模糊综合评判的方法进行水力压裂井优选.通过对影响压裂效果的各个因素进行分析,优选出生产压差、含水率、压前增油量、孔隙度、渗透率、小层有效厚度、加砂量等7个主要因素,并应用层次分析法得到各个影响因素的权重,最后采用模糊综合评判方法对水力压裂井进行评估,最终判定其是否适合压裂并对压裂井进行优选,现场实际应用表明,该方法可以提高现场的工作效率和选井的客观性、准确性.     

固体边壁上点面脉动压力转换的数学推导

利用相关分析方法 ,详细讨论了作用于水工建筑物的平面、柱面和球面上的边壁脉动压力的点面转换关系 ,推导出面脉动荷载的解析表达式 .该成果对工程设计工作具有指导意义     

求函数项级数收敛区间的一种新方法

对形如∑∞n=0anxkn+b(k∈,b∈)的幂级数,当其缺项的时候,不能直接用公式ρ=li mn→∞an+1an求其收敛半径与收敛区间(本文约定收敛区间不含端点),一般都是直接采用达朗贝尔(比值)判别法求其收敛半径与收敛区间.事实上,对这种幂级数只需先作一个变量代换,就可以采用公式法求解.本文给出了这种方法的理论证明,并将结论进行了推广,即利用变量代换与公式法同样可求形如∑∞anxkn+bs(k,s∈,b∈)形式的函数项级数的收敛区间.     

Modelling of a Switching Control Hydraulic System

Modelling of a hydraulic system featuring a specific type of switching control is presented. Despite conventional hydraulic drive technology where rather smooth changes of pressure and flow rate are intended and where oscillations constitute undesired phenomena, switching control provokes oscillations as an indispensable element to achieve high energetic efficiency with valve control. The system under study is one which comprises a novel switching valve, a long line with considerable wave propagation dynamics, a hydraulic cylinder, and the valve's dynamics.     

Numerical stability of the BEM for advection‐diffusion problems

A boundary element method (BEM) approach has been developed to solve the time‐dependent 1D advection‐diffusion equation. The 1D solution is part of a 3D numerical scheme for solving advection‐diffusion (AD) problems in fractured porous media. The full 3D scheme includes a 3D solution for the porous matrix, which is coupled with a 2D solution for fractures and a 1D solution for fracture intersections. As the hydraulic conductivity of the fracture intersections is usually higher than the hydraulic conductivity of the fractures and by at least one order of magnitude higher than the hydraulic conductivity of the porous matrix, the fastest flow and solute transport occurs in the fracture intersections. Therefore it is important to have an accurate and stable 1D solution of the transient AD problems. This article presents two different 1D BEM formulations for solution of the AD problems. The particular advantage of these formulations is that they provide one of the most straightforward and simplest ways to couple multiple intersecting 2D Boundary Element problems discretized with linear discontinuous elements. Both formulations are tested and compared for accuracy, stability, and consistency. The analysis helps to select the more suitable formulations according to the properties of the problem under consideration. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2004     

Two-stream counter-flow heat exchanger equation with time-varying velocities

We study the two-stream counter-flow heat exchanger equation with time-varying fluid velocities. Formulating it into a time-varying boundary control system, a representation formula of the solution is obtained.     

ERROR ESTIMATES FOR SPARSE OPTIMAL CONTROL PROBLEMS BY PIECEWISE LINEAR FINITE ELEMENT APPROXIMATION

Optimization problems with L¹-control cost functional subject to an elliptic partial differential equation(PDE)are considered.However,different from the finite dimensiona l¹-regularization optimization,the resulting discretized L¹norm does not have a decoupled form when the standard piecewise linear finite element is employed to discretize the continuous problem.A common approach to overcome this difficulty is employing a nodal quadrature formula to approximately discretize the L¹-norm.In this paper,a new discretized scheme for the L¹-norm is presented.Compared to the new discretized scheme for L¹-norm with the nodal quadrature formula,the advantages of our new discretized scheme can be demonstrated in terms of the order of approximation.Moreover,finite element error estimates results for the primal problem with the new discretized scheme for the L¹-norm are provided,which confirms that this approximation scheme will not change the order of error estimates.To solve the new discretized problem,a symmetric Gauss-Seidel based majorized accelerated block coordinate descent(sGS-mABCD)method is introduced to solve it via its dual.The proposed sGS-mABCD algorithm is illustrated at two numerical examples.Numerical results not only confirm the finite element error estimates,but also show that our proposed algorithm is efficient.     

A semi-analytic pricing formula for lookback options under a general stochastic volatility model

In general, the pricing problems of exotic options in finance do not have analytic solutions under stochastic volatility and so it is hard to compute the option prices or at least it requires much of time to compute them. This paper investigates a semi-analytic pricing method for lookback options in a general stochastic volatility framework. The resultant formula is well connected to the Black–Scholes price that is the first term of a series expansion, which makes computing the option prices relatively efficient. Further, a convergence condition for the expansion is provided with an error bound.     

两个不同Gauss和的混合均值

本文利用解析方法以及三角和的性质研究两个不同Gauss和的混合均值的计算问题,并给出一个精确的计算公式.作为我们结果的应用,得到了关于模p的一类对角同余方程解的个数的计算公式,其中p是一个奇素数.