Modeling and simulation of cavitation in hydraulic pipelines based on the thermodynamic and caloric properties of liquid and steam

The present paper focuses on a homogeneous cavitation model based on the thermodynamic equilibrium model of liquid and steam, which has significant importance for the development of modern hydraulic tools and injection systems. Subsequent to the derivation of the mathematical model a numerical method is described. Computations are carried out for a variety of test cases. The results are compared with analytic solutions, experimental data, and simulations obtained with a different numerical scheme. The investigation proves the ability of the method to predict cavitation in hydraulic pipelines in a reliable and successful manner. The lucidity of the procedure enables a simple extension of the model and the numerical method to higher space dimensions as well as applications in the context of complex hydraulic systems.Received: 2 May 2002, Revised: 7 July 2003, Accepted: 5 August 2003, Published online: 18 February 2005[/PUBLISHED]Correspondence to: A. Meister     

Strong discontinuities in spatial stationary long-wave flows of an ideal incompressible fluid

Spatial stationary flows over an even bottom of a heavy ideal fluid with a free surface are considered. Jump relations for flows with a strong discontinuity are studied. It is shown that the flow parameters behind the jump are defined by a certain curve which is an analog of the (θ, p) diagram in gas dynamics. A shock polar and examples of flows with a hydraulic jump are constructed for a particular class of solutions. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 37–45, March–April, 2009.     

Bail-Down Test Simulation at Laboratory Scale

This paper presents a comparison of hydraulic oil conductivity obtained from interpreting bail-down test data to values calculated from theory. The bail-down tests were performed at laboratory scale, on a radial portion of a circular domain filled with calibrated sand allowing hydraulic oil conductivity to be calculated using Parker’s theoretical model (Parker et al. in Water Resour Res 23(4):618–624, 1987). The bail-down tests were interpreted using the modified Bouwer and Rice (Huntley in Ground Water 38(1):46–52, 2000) and the modified Cooper methods (Beckett and Lyverse in API Interact LNAPL Guide 2:1–27, 2002). The results show that (1) both interpretation methods from bail-down test data give similar hydraulic oil conductivities, and (2) the hydraulic oil conductivities estimated from bail-down test data agree well with the hydraulic oil conductivity predicted when using the Parker theoretical model. Overall, this paper confirms that the modified Bouwer and Rice (Huntley 2000) and the modified Cooper methods (Beckett and Lyverse 2002) are valid to estimate hydraulic oil conductivity, giving realistic values despite test conditions not meeting all the assumptions and boundary conditions of each analytical solution.     

Moisture Absorption in Capillary Active Materials: Analytical Solution for a Multiple Step Diffusivity Function

This paper deals with the double-constraint methodology for calibration of steady-state groundwater flow models. The methodology is based on updating the hydraulic conductivity of the model domain by comparing the results of two forward groundwater flow models: a model in which known fluxes are specified as boundary conditions and a model in which known heads are specified as boundary conditions. A new zone-integrated double-constraint approach is presented by partitioning the model domain in zones with presumed constant hydraulic conductivity (soft data), and the double-constraint methodology is reformulated accordingly. The feasibility of the method is illustrated by a practical case study involving a numerical steady-state groundwater flow model with about 3 million grid blocks, subdivided into four zones corresponding to the major hydrogeological formations. The results of the zone-integrated double-constraint method for estimating the horizontal and vertical hydraulic conductivities of the zones compare favourably with a classical model calibration based on minimisation of the differences between calculated and measured heads, while the double-constraint method proves to be more robust and computationally less cumbersome.     

2D shallow water flow model for the hydraulic jump

A flow model is presented for predicting a hydraulic jump in a straight open channel. The model is based on the general 2D shallow water equations in strong conservation form, without artificial viscosity, which is usually incorporated into the flow equations to capture a hydraulic jump. The equations are discretised using the finite volume method. The results are compared with experimental data and available numerical results, and have shown that the present model can provide good results. The model is simple and easy to implement. To demonstrate the potential application of the model, several hydraulic jumps occurring in different situations are simulated, and the predictions are in good agreement with standard solution for open channel hydraulics. Copyright © 1999 John Wiley & Sons, Ltd.     

A Geometrical Pore Model for Estimating the Microscopical Pore Geometry of Soil with Infiltration Measurements

This paper presents a simple geometrical pore model designed to relate characteristic pore radii of the porous network of soils with macroscopic infiltration parameters. The model composed of a stack of spherical hollow elements is described with two radii values: the pore access radius and the actual pore radius. The model was compared to cylindrical pore models and its mathematical consistency was assessed. Soil sorptivity S and the second parameter A of the Philip infiltration equation (1957), have been determined by numerically simulated infiltration. A diagram and an empirical relation have been set in order to relate the pore access and pore radii to the infiltration parameters S and A. The consistency of the model was validated by comparing the predicted sorptivity and hydraulic conductivity values, with the widely used unsaturated soil hydraulic functions (van Genuchten, 1980). The model showed good agreement with experimental infiltration data, and it is therefore concluded that the use of a model with two radii improves the relation between microscopic pore size and macroscopic infiltration parameters.     

Force prediction equation using distorted model as an analog device

The force versus speed response of a distorted model of a soil-engaging tool operating in a soil and at a depth where the performance evaluation of the prototype is required to be determined, is used to compute analog values. A prediction equation relating draft force with tool width, depth of cut, soil specific weight, tool velocity and analog values has been developed. A comparison between the forces predicted by the equation and that measured on flat rectangular blades and angled tools operating at a speed of 2–8.5 km/hr is presented. The closeness in prediction accuracies points that the distorted model itself can be used as a fairly good analog device.     

Quantitative flow visualization using the hydraulic analogy

The current work describes the development of a non-intrusive optical method for the quantitative determination of water heights along a hydraulic jump in shooting water flows on a water table. The technique involves optically superimposing a series of alternating dark and clear fringes on the water flow. It is proposed that the fringe deviations seen under a hydraulic jump can be simulated using a series of optical prisms oriented along the direction of the hydraulic jump. The height of each prism gives the local maximum water height at the fringe location. Three types of theoretical prism configurations (isosceles flat-topped prism, scalene flat-topped prism and rounded-topped prism models) have been studied for two flow systems: shooting flow around a wedge and around a cylinder. Equations relating the physical characteristics of the deviated fringes to the height of the theoretical prism and hence the local water height are presented. The variation in water height along a hydraulic jump for flow around a wedge obtained using the optical technique has been compared with heights obtained using a depth gauge. The results were in good agreement for the range of Froude numbers studied (Fr=1.9−3.6). The rounded-topped prism model led to the best agreement with the physical measurements, within 11% throughout the range of conditions studied. The uncertainty associated with the water height determination using the optical technique is ±10%. Received: 15 September 1998/Accepted: 16 April 1999     

Enhancing the Bolzon–Schrefler–Zienkiewicz Constitutive Model for Partially Saturated Soil

This paper presents an enhanced version of the elasto-plastic model for partially saturated soil first proposed by Bolzon, Schrefler and Zienkiewicz in 1996, “BSZ” model, which uses the effective stress tensor and suction as independent stress variables. It is recalled that the effective stress tensor proposed by Lewis and Schrefler in 1982 is thermodynamically consistent and, compared with other choices of stress tensors, results particularly suitable for partially saturated soil mechanics. A hydraulic constitutive relationship and a hydraulic hysteresis are introduced in the model, to take into account the irreversible deformation during cyclic drying and wetting until structural collapse. For this reason the plastic rate of strain is split into the sum of two components: one depending on the effective stress tensor and the other one on suction. This is the new feature of the BSZ model. This enhanced model is then cast into a thermodynamical framework at macroscopic level and it is shown that it is possible to derive the constitutive law from the Helmholtz free energy and a dissipation function, both for associative and non- associative plasticity. Finally the model predictions have been compared with experimental data for Sion slime, with particular emphasis on the deviatoric part, and model predictions of hysteretic behaviour have been investigated in case of a wetting and drying cycle on compacted betonite–kaolin.     

Dynamical analysis of an improved FitzHugh-Nagumo neuron model with multiplier-free implementation

The cubic-polynomial nonlinearity with N-shaped curve plays a crucial role in generating abundant electrical activities for the original FitzHugh-Nagumo (FHN) neuron model. The pioneer FHN neuron model is efficient in theoretical analysis and numerical simulation for these abundant electrical activities, but analog multipliers are indispensable in hardware implementation since the involvement of cubic-polynomial nonlinearity. Analog multiplier goes against the circuit integration of FHN neuron model due to its huge implementation costs. To avoid the involvement of analog multiplier in hardware implementation, a nonlinear function possessing N-shaped curve and multiplier-free implementation is presented in this paper. To confirm the availability of this nonlinear function in generating electrical activities, numerical simulations and hardware experiments are successfully executed on an improved two-dimensional (2D) FHN neuron model with externally applied stimulus. The results demonstrate that the improved FHN neuron model can generate rich electrical activities of periodic spiking behavior, chaotic behavior, and quasi-periodic behavior. Analog circuit implementation without any multiplier and its hardware experiment show the availability of the proposed nonlinear function, which is appropriate for analog circuit implementation of FHN neuron-based neuromorphic intelligence.

     

页岩气藏压裂缝网扩展数值模拟

为探究页岩气藏水力压裂复杂裂缝网络的形成机理,开展了缝网扩展的数值模拟研究.考虑应力阴影和天然裂缝作用,建立了井筒和裂缝中流体流动模型,利用位移不连续方法求解应力与位移不连续量,然后构建了压力与裂缝宽度的迭代方程,并采用牛顿迭代法求解.通过比较数值解经典模型解析解,验证了模型和迭代解法的正确性.多簇裂缝同步扩展时裂缝间距越小,压裂液分配到各条裂缝越不均匀,靠近井筒跟部的裂缝的分流量越大,从而裂缝宽度越大;考虑天然裂缝作用时,逼近角越小或者应力各向异性越弱,水力裂缝越容易发生转向扩展,裂缝网络越复杂.      

Two photoviscoelasticity experiments using analog data reduction

A tensile analog may conveniently be used to determine the history of the principal-stress difference from the results of some photoviscoelastic model tests. With this method, the model test is run, and the fringe-order history at the point (s) of interest in the model is recorded. A tensile specimen of the same material is placed in a loading frame and loaded with a stress history which forces it through the fringe-order history observed in the model. This stress history is then the desired principal-stress-difference history occurring in the model. The stress history at points in two nonhomogeneous models was determined with a tensile analog. The uses and limitations of the analog technique are discussed.     

A 3D DEM-LBM approach for the assessment of the quick condition for sands

We present a 3D numerical model to assess the quick condition (the onset of the boiling phenomenon) in a saturated polydisperse granular material. We use the Discrete Element Method (DEM) to study the evolution of the vertical intergranular stress in a granular sample subjected to an increasing hydraulic gradient. The hydrodynamic forces on the grains of the sample are computed using the Lattice Boltzmann Method (LBM). The principal assumption used is that grains remain at rest until the boiling onset. We show that the obtained critical hydraulic gradient is close to that defined in classical soil mechanics. To cite this article: M. Mansouri et al., C. R. Mecanique 337 (2009).     

Modeling air entrainment and transport in a hydraulic jump using two-fluid RANS and DES turbulence models

Both RaNS (Reynolds-averaged Navier–Stokes) and DES (Detached Eddy Simulation) type turbulence models were used in conjunction with a two-fluid model of bubbly flow and a new subgrid air entrainment model to predict air entrainment and transport in a hydraulic jump. It was found that the void fraction profiles predicted by both methods are in agreement with the experimental data in the lower shear layer region, which contains the air bubbles entrained at the so-called toe of the hydraulic jump. In contrast, in the upper roller region behind the toe, the averaged results of the DES turbulence model gives accurate predictions while a RaNS turbulence model does not. This is because the DES turbulence model successfully captures the strong fluctuations on the free surface which allows it to entrain air near the top of the roller region. In contrast, RaNS type turbulence model results in a steady, smooth interface which fails to capture the wave-induced bubble sources in that region. To our knowledge, this study is the first successful quantitative numerical simulation of the overall void fraction profiles in a hydraulic jump.     

Attenuation analysis of hydraulic transients with laminar-turbulent flow alternations

An improved compound mathematical model is established to simulate the attenuation of hydraulic transients with laminar-turbulent alternations,which usually occur when the pipeline flow velocity fluctuates near the critical velocity.The laminar friction resistance and the turbulent friction resistance are considered respectively in this model by applying different resistance schemes to the characteristics method of fluid transient analysis.The hydraulic transients of the valve closing process are simulated using the model.A more reasonable attenuation of hydraulic transients is obtained.The accurate attenuation is more distinct than that obtained from the traditional mathematical model.The research shows that the hydraulic transient is a type of energy waves,and its attenuation is caused by the friction resistance.The laminar friction resistance is more important than the turbulent friction resistance if the flow velocity is smaller than the critical velocity.Otherwise the turbulent friction resistance is more important.The laminar friction resistance is important in the attenuation of hydraulic transients for the closing process.Thus,it is significant to consider the different resistances separately to obtain more accurate attenuation of hydraulic transients.     

岩质边坡稳定性及预应力锚固分析现状

本文首先对目前常用的各类边坡稳定性分析方法的主要特点进行了评述,包括定性方法类的历史分析法、工程地质类比法、图解法、专家系统法,定量分析方法类的确定性模型法,如极限平衡法,应力应变分析法;非确定性模型法,如可靠性分析法、灰色系统理论法及模糊综合评判法等;及两类方法结合而成的随机有限元法。其次,对预应力锚固边坡的设计及稳定性分析作了阐述。     

液压减振器随机热力学模型与油温变化研究

为了获得具有更多信息和更加接近工程实际的液压减振器油温热力学模型,将随机不确定性理论引入到液压减振器油温传统热力学模型中进行研究。将液压油密度、导热系数、比热容和运动粘度作为随机变量,运用求解函数数字特征的代数综合法建立减振器随机热力学模型,进而获得油液传热过程规律。将油温随机热力学模型研究结果和传统模型的计算结果与实验结果进行比较,证明随机不确定性理论的引入可行且随机热力学模型比传统模型更加优越。     

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在仿真研究1/4车体二自由度液压半主动悬架的基础上,设计了一种 用于1/2车体的液压半主动悬架的参数自整定模糊PID控制器,并利用模糊控制规则对 PID参数进行在线修改. 以正弦信号路面、脉冲信号路面和C级路面3种典型路面作为输入 信号,应用MATLAB/Simulink控制系统仿真软件对该半主动悬架模型进行的计算机仿真表明, 具有模糊PID控制器的半主动悬架在提高车辆乘坐的舒适性方面要明显优于一般的模糊控制 悬架,具有更好的自适应能力.     

页岩气高效开采中钻井完井和水力压裂的关键力学问题

本文研究了在页岩气高效开采中钻井完井和水力压裂缝网改造的关键力学问题. 提出了页岩多孔弹性介质的本构、强度和断裂韧性的各向异性模型, 指出了微观均匀假设与微观各向同性假设在页岩多孔弹性本构中的简化应用, 给出了横观各向同性多孔弹性岩石材料常数的简化测量方案, 讨论了基于修正的能量最大释放率下裂纹扩展的弱面模型, 提出了裂纹扩展禁止区现象. 阐述了钻井完井过程中的多孔弹性介质井壁稳定性和剪切破坏的时间效应, 提供了多种破坏模式下井壁许可压力范围的显式表达式, 并与传统广义胡克定律得到结果对比. 给出了水平井水力压裂缝网改造技术, 包含水力压裂的大物模实验技术、水力压裂过程中基于扩展有限元与有限体积法的耦合流体/固体/裂缝扩展的数值模拟方法, 并与黏性主导的水力压裂解析解结果对比, 针对性分析了川渝地区的水力压裂施工现场实践应用问题. 建立了基于数据驱动的页岩气采收率预测方法, 指出了机器学习中极限梯度爬升法在小数据集情况下的有效性.      

基于孔隙弹性的水力压裂耦合方法与压裂状态参数数值研究

本文系统地阐述基于多孔介质渗流-损伤耦合原理,进行水力压裂FEM的数值实现方法。基本架构为：(1)引入孔隙流体压力膨胀系数将孔隙流体压力与应力场进行耦合;(2)基于损伤局部化模型,提出裂缝张开度表达式; (3)提出水力压裂引起的多孔介质水-力学属性的各向异性表达式; (4)提出全流量加载的耦合分析方案。最后作为实例,模拟三维地层水压裂缝扩展形态,通过比较模型的数值解和经典理论解,验证该方法的正确性。