Compared techniques for the critical submergence of an intake in water flow

Air-entraining vortex at intake is an important problem encountered in hydraulic engineering. Intake submergence depth could result in formation of the air-entraining free surface vortices. Unless the dangerous air entrainment is eliminated, air entraining causes mechanical damage, vibration in pipelines and loss of pump performance. The value of the intake’s submergence when the vortex starts entraining air is known as “critical submergence”. In this study, the critical submergence for a circular intake pipe in still-water and open channel flow for permeable and impermeable bottom was investigated. Experimental results were used to compare with critical spherical sink surface (CSSS), radial basis function based neural network (RBNN) and general linear model (GLM). The CSSS has the same center and discharge as the intake with the critical submergence. The GLM underlies most of the statistical analyses that are used in applied research. And the RBNN is one of the most used network models. The ranking of prediction on critical submergence is obtained as RBNN, GLM and CSSS, respectively.     

Numerical Analysis of a Vortex Tube: A Review

Ranque–Hilsch vortex tube is a simple devise with no moving parts which could generate cold and hot air/gas streams simultaneously with compressed air/gas as a working fluid. The energy and flow separation in a vortex tube is highly depends on factors like nozzle shape, nozzle number, diameter and length of the vortex tube, inlet pressure, control valve, diaphragm hole size and cold mass fraction. As the energy separation and flow patterns in a vortex tube are highly complex and were not explained successfully by any researcher, a computational study of vortex tube flow and energy separation will give a better understanding about the physics and mechanism involved. Many researchers conducted computational fluid dynamic analysis of the vortex to have a deep insight about the process of flow separation. In this paper computational analysis of vortex by many researchers were presented along with the results obtained and suggestions to improve the performance of the vortex tube. Researchers considered Turbulence models which predict the performance precisely were discussed in the present paper. Researchers considered turbulence models like LES, k–ε, k–ω and RMS to predict the energy separation in vortex tube. Some researchers considered artificial neural networks (ANN) and Taguchi methods for their analysis. Comparison of the predictions with simulation results were also presented to give a clear idea for the reader about the CFD models prediction capabilities.     

基于环形管差压波动信号测量气液两相流气相含率的研究

设计了一种新型多圈环形管用于气液两相流参数的测量,对环形管上升段水平方向内外侧差压波动信号进行了分析,采用无因次分析方法获得与差压波动信号均方根相关的特征量,建立了此特征量与容积含气率的关系模型,并在此基础上进行了实验.实验结果表明与差压波动信号均方根有关的特征量和容积含气率存在一定的关系,在考虑到气体密度的影响之后,引入气体密度对关系模型进行修正,建立了差压波动信号均方根和容积含气率量纲1的线性关系模型.在容积含气率小于0.65时,气液两相流的容积含气率测量误差小于5%,为气液两相流的容积含气率测量提供了一种方法.     

Using the artificial neural network model for modeling the performance of the counter flow vortex tube

In this study, the effect of the nozzle number and the inlet pressure on the heating and cooling performance of the counter flow type vortex tube has been modeled with artificial neural networks (ANN) by using the experimentally obtained data. ANN has been designed by Pithiya software. In the developed system output parameter temperature gradient between the cold and hot outlets (ΔT) has been determined using inlet parameters such as the inlet pressure (P_inlet), nozzle number (N), and cold mass fraction (μ_c). The back-propagation learning algorithm with variant which is Levenberg–Marquardt (LM) and Fermi transfer function have been used in the network. In addition, the statistical validity of the developed model has been determined by using the coefficient of determination (R²), the root means square error (RMSE) and the mean absolute percentage error (MAPE). R², RMSE and MAPE have been determined for ΔT as 0.9947, 0.188224, and 0.0460, respectively.     

径向基神经网络在近似建模中的应用研究

为了在不依赖测试样本的前提下获取最优的径向基函数分布系数Opt_SPRD,从而构造出具有更高精度的径向基神经网络（RBNN）近似模型,提出了一种基于交叉验证的分布系数选取方法。该方法以分布系数与交叉验证误差之间的函数为基础,把对应于交叉验证误差最小值的分布系数作为Opt_SPRD的近似解。数值实验的结果表明,所提出的方法明显优于目前通行的缺省处理方法;与基于L-M BP算法的前馈神经网络近似模型相比,在所提出方法基础上构造出的RBNN近似模型具有更高、更稳定的精度。     

超临界CO2流体中空化泡动力学过程分析

考察各参数影响超临界CO2流体中超声空化动力学过程的规律.应用非线性Rayleigh-Plesset方程模拟空化泡运动过程,利用Matlab软件编程求数值解,结果:空化泡初始半径或超声波频率增大,空化变易,强度变弱;超声波的声压幅值增大.空化变易,强度变强;超临界CO2流体的压力的增大,空化变难,强度变弱;温度不会影响空化的难易程度,只是随着温度升高,强度变强.     

A numerical investigation of fluid flow over a rotating cylinder with cross flow oscillation

This paper studies a two-dimensional incompressible viscous flow past a rotating cylinder with cross flow oscillation using a finite element method based on the characteristic based split (CBS) algorithm to solve governing equations including full Navier–Stokes and continuity equations. Dynamic unstructured triangular grid is used employing lineal and torsional spring analogy which is coupled with the solver by an Arbitrary Lagrangian–Eulerian (ALE) formulation. After verifying the accuracy of the numerical code, simulations are conducted for the flow past a rotating cylinder with cross flow oscillation at moderate Reynolds numbers of 50, 100, and 200 considering different non-dimensional rotational speeds based on the free-stream velocity in the range 0–2.5, and various oscillating amplitudes and frequencies. Effects of the oscillation and rotation of the cylinder on the vortex shedding both in lock-on and non-lock-on regions, the mean drag and lift coefficients, and the Strouhal number are investigated in detail. It is found that similar to the fixed cylinder beyond a critical non-dimensional rotational speed the vortex shedding is highly suppressed. In addition, by increasing the rotational speed of the cylinder, the lift coefficient increases while decreasing the drag coefficient. However, in the vortex lock-on region both the lift and the drag coefficients increase significantly.     

Effects of pressure impulse and peak pressure of a shockwave on microjet velocity in a microchannel

We experimentally investigate the effect of a shockwave on the velocity of a microjet and underwater cavitation onset in a microchannel, focusing on the pressure impulse and peak pressure of the shockwave. The pressure impulse and peak pressure of the shockwave are separately varied by using non-spherical laser-induced shockwaves (Tagawa et al. in J Fluid Mech 808:5–18, 2016). We conduct two kinds of experiments. In one experiment, we install a narrow tube and a hydrophone in different configurations in large water-filled tank. We measure the shockwave pressure and the jet velocity simultaneously in order to elucidate the effects of pressure profile of shockwaves on the jet velocity. In the other experiment, we record the jet formation and cavitation onset to investigate the effect of cavitation onset on the jet velocity in an L-shaped microchannel. The experimental results suggest that the jet velocity depends only on the pressure impulse of the shockwave, while the probability of cavitation onset depends only on the peak pressure of the shockwave. The above findings provide new insights for advancing a control method for high-speed microjets.     

基于线列阵传感器的射流冲击试验含气率分布研究

射流冲击是一种气-液两相流现象,既可作为一种除盐水混合硼酸的有效方法,也可用于研究压水堆（PWR）的承压热冲击（PTS）事故现象。当液体射流撞击水面时,发生气体夹带现象,并产生气泡,气泡夹带对混合过程起到关键的影响作用。研究了不同射流高度和流速下的含气率分布,设计了一种新型三层可移动线列阵传感器（WMS）测量瞬时二维局部空隙率,具有较高的空间分辨率（3 mm）和极高的时间分辨率（2500 Hz）,基于线列阵传感器测量的原始数据,获得了射流冲击中气体夹带的含气率分布,对比分析了不同射流高度和流速下的平均含气率分布。     

Flow of CO<Subscript>2</Subscript>–ethanol and of CO<Subscript>2</Subscript>–methanol in a non-adiabatic microfluidic T-junction at high pressures

In this work, an experimental investigation of the single- and multiphase flows of two sets of fluids, CO₂–ethanol and CO₂–methanol, in a non-adiabatic microfluidic T-junction is presented. The operating conditions ranged from 7 to 18 MPa, and from 294 to 474 K. The feed mass fraction of CO₂ in the mixtures was 0.95 and 0.87, respectively. Under these operating conditions, CO₂ was either in liquid, gas or supercritical state; and the mixtures experienced a miscible single phase or a vapour–liquid equilibrium (VLE), with two separated phases. Taylor, annular and wavy were the two-phase flow regimes obtained in the VLE region. In the single phase region, the observed flows were classified into standard single-phase flows, “pseudo” two-phase flows and local phenomena in the T-junction. Flow regime maps were generated, based on temperature and pressure conditions. Two-phase flow void fractions and several parameters of Taylor flow were analysed. They showed a clear dependency on temperature, but were mostly insensitive to pressure. A continuous accumulation of liquid, either in the CO₂ channel or at the CO₂-side wall after the T-junction, disturbed most of the experiments in VLE conditions by randomly generating liquid plugs. This phenomenon is analysed, and capillary and wetting effects due to local Marangoni stresses are suggested as possible causes.     

Neuro-fuzzy based constitutive modeling of undrained response of Leighton Buzzard Sand mixtures

This study aims to develop neuro-fuzzy (NF) based constitutive model for Leighton Buzzard Sand fraction B and Leighton Buzzard Sand fraction E mixtures using experimental data. The experimental database used for NF modeling is based on a laboratory study of saturated mixtures with various mix ratios under a 100 kPa effective stress. Emphasis was placed on assessing the role of fines content in mixture and strain level on the deviatoric stress and pore water pressure generation in a 100 mm diameter triaxial testing apparatus. The input variables in the developed rule based NF models are the Leighton Buzzard Sand fraction E content, and strain, and the outputs are deviatoric stress, pore water pressure generation and undrained Young’s modulus. Experimental results show that Leighton Buzzard Sand fraction B and Leighton Buzzard Sand fraction E mixtures exhibits clay-like behavior due to particle–particle effects with the increase in Leighton Buzzard Sand fraction E content. It is also shown that the performance of capacities of proposed NF models are quite satisfactory.     

Assessing the impacts of South-to-North Water Transfer Project with decision support systems

The South to North Water Transfer Project is one of the four largest trans-century projects in China, which is expected to be completed by 2008. The project seeks to promote Northern China's economic growth by relaxing water constraints in a region now facing severe water shortage. In this paper, a decision support system (DSS) for assessing the social–economic impact of China's South-to-North (S2N) Water Transfer project is presented. The DSS provides decision support through simulation with an embedded water computable general equilibrium model (WCGE). The system is able to perform qualitative analysis on regional water resource vulnerability with mathematical modeling. In addition, the system is also able to examine a region's water demand–supply balance dynamics through forecasting with the WCGE model on the basis of various scenarios for the time horizon up to the year 2020. The what-if analysis performed by the DSS shows that the incremental water supply from the project helps the recipient region to catch up with the development pace of the country as a whole.     

A generalized continuous surface tension force formulation for phase-field models for multi-component immiscible fluid flows

We present a new phase-field method for modeling surface tension effects on multi-component immiscible fluid flows. Interfaces between fluids having different properties are represented as transition regions of finite thickness across which the phase-field varies continuously. At each point in the transition region, we define a force density which is proportional to the curvature of the interface times a smoothed Dirac delta function. We consider a vector valued phase-field, the velocity, and pressure fields which are governed by multi-component advective Cahn–Hilliard and modified Navier–Stokes equations. The new formulation makes it possible to model any combination of interfaces without any additional decision criteria. It is general, therefore it can be applied to any number of fluid components. We give computational results for the four component fluid flows to illustrate the properties of the method. The capabilities of the method are computationally demonstrated with phase separations via a spinodal decomposition in a four-component mixture, pressure field distribution for three stationary drops, and the dynamics of two droplets inside another drop embedded in the ambient liquid.     

运输类大型飞机噪声适航测试方法应用

对研发过程中的新舟700系列飞机在内的涡桨运输类客机的噪声适航方法进行分析,对其瞬时声压级、有效感觉噪声级等算法进行研究.使用丹麦B&K公司的噪声分析产品PLUSE声学测试分析系统,采用基于静态测试预测噪声级的算法,“以机代台”对发动机静态数据进行分析.利用涡桨类飞机竞争机型庞巴迪DHC-8-400飞机已有的噪声数据,使用C#语言和Visual Studio 2013平台开发预测系统.最后利用SPSS软件进行置信区间的计算,验证数据的符合性.方法及竞争机型噪声数据可为今后上市的涡桨类运输飞机提供噪声适航研发依据.     

旋转固体火箭发动机统一流场计算

为了进一步研究旋转对固体火箭发动机工作的影响,采用RSM湍流模型对内孔燃烧、内孔与端面同时燃烧管状装药旋转固体火箭发动机统一流场进行了仿真。采用UDF编程给出质量入口边界,获得了旋转条件下发动机内流场结构参数特点,并给予理论说明。计算结果表明,内孔燃烧装药发动机切向速度流场类似于典型的Rankine涡,端面和内孔同时燃烧装药发动机切向速度流场呈现出Rankine涡和由端面燃烧引起的强迫涡的复杂组合涡;在发动机前封头和喷管喉部涡核切向速度峰值非常大,使燃烧室前封头和喷管喉部工作环境显著恶化;旋转使发动机燃烧室压力沿径向逐渐增大,强迫涡附近的压力梯度远大于推进剂表面的压力梯度。     

Upstream wake-secondary flow interactions in the endwall region of high-loaded turbines

A detailed experimental and numerical investigation of the unsteady interaction of secondary flow vortices in turbine endwall region was performed with the effect of upstream periodic wakes. The flow field was investigated respectively in a linear turbine cascade and a turbine rotor. The study revealed the physical mechanisms of unsteady interaction between upstream wake and secondary vortices. The influence of the upstream wake on the performance of turbine endwall region was also discussed.The flow field at the exit of the turbine blade row showed a decrease in passage vortex strength and loss due to the upstream wake transport. Two interaction mechanisms are proposed whereby passage vortex loss decreases. They are the upstream wake-pressure side leg of the horseshoe vortex interaction and the upstream wake-passage vortex interaction. The transport of upstream wake can suppress the development of pressure side leg of the horseshoe vortex and passage vortex because of the “negative jet” influence of the wake.     

Evaluation of peak and residual conditions of actively confined concrete using neuro-fuzzy and neural computing techniques

This paper investigates the ability of four artificial intelligence techniques, including artificial neural network (ANN), radial basis neural network (RBNN), adaptive neuro-fuzzy inference system (ANFIS) with grid partitioning, and ANFIS with fuzzy c-means clustering, to predict the peak and residual conditions of actively confined concrete. A large experimental test database that consists of 377 axial compression test results of actively confined concrete specimens was assembled from the published literature, and it was used to train, test, and validate the four models proposed in this paper using the mentioned artificial intelligence techniques. The results show that all of the neural network and ANFIS models fit well with the experimental results, and they outperform the conventional models. Among the artificial intelligence models investigated, RBNN model is found to be the most accurate to predict the peak and residual conditions of actively confined concrete. The predictions of each proposed model are subsequently used to study the interdependence of critical parameters and their influence on the behavior of actively confined concrete.

     

古田溪水电厂三级2 号机组尾水管改造

本文介绍了古田溪水力发电厂三级电站2号机组尾水管改造工程,改造内容主要包括:(1)尾水管局部更新;(2)尾水进人门更新;(3)尾水管基础灌浆。     

Modified T–Z model-a software for tension piles

Pile foundation is one of the common type of foundation used to support structures resting in weak soils and in an offshore environment. Piles are generally subjected to compressive (downward) loads. Hence, the majority of studies on piles are directed towards their behaviour under compressive loads. With the development of tension leg platform (TLP) technology for developing deep offshore oil and gas fields, there is a growing interest in understanding TLP pile foundation. The piles used for TLP foundation are subjected to static pull-out force superimposed by a cyclic tensile force.The review of literature shows that the T–Z method proposed by Sulaiman and Coyle is being used commonly to estimate the load–displacement behaviour of tension piles. Although the method is simple, it suffers from few limitations.This paper critically review the model suggested by Sulaiman and Coyle and presents a modified T–Z model for tension piles. Details of a computer program developed, for the modified T–Z model, are presented in the form of flow-chart and algorithm. The program developed is employed to estimate load–displacement behaviour of a set of field piles. The results are compared with the observed values and with those predicted by the Sulaiman and Coyle method. It is observed that the modified T–Z model provides a better prediction to the observed values than those predicted by the model suggested by Sulaiman and Coyle.     

On Estimation of Information via Variation

New inequalities relating mutual information and variational distance are derived.__________Translated from Problemy Peredachi Informatsii, No. 2, 2005, pp. 3–8.Original Russian Text Copyright © 2005 by Pinsker.A draft version of the paper was found in the author’s archive. The Editorial Board thanks M.V. Burnashev for careful preparation of the text.