The Discuss of the Formula of Flow Loss and Water Using Coefficient on Seepage Proofed Channel

On the basis of the analysis about present water resource situation in China,the disadvantage of the for- mula of flow loss and water using coefficient on anti-seep channel which have been applying in channel de- sign and water saving irrigation administration will be indicated in the paper. The characteristics of that the loss of conveying water is changeable with the now changing have been take into account in the new formula. The formula is validated by the example of middle permeable channel (A=1.90,m=0.40). The calculate re- sult is more precision. Also some formula has been given,they can be referred to the worker of the irrigation administration.

Automatic pipes routing based on flow loss in electromechanical product

Based on flow loss,a new automatic pipe-routing algorithm is proposed for electromechanical product in 3D space,which consists of pre-processing and optimization search.Utilizing chaos theory,a chaos grid pre-processing model (CGPM) is established to efficiently pick up the solution space and reduce the search range in the pre-processing,which simplifies the optimization search.A modified particle swarm optimization (PSO) algorithm is presented to seek for an approximate optimal trajectory in the solution space in the optimization search based on standard PSO algorithm and migration characters of people.The comparison of experiments and analysis results shows that the modified PSO algorithm is capable of preventing prematurity effectively and searching for the optimal trajectory more efficiently.Theoretical analysis proves that the modified PSO algorithm converges at global optimum.The examples show that the automatic pipe-routing algorithm based on flow loss is effective and practical for electromechanical product.

Flow Loss Mechanism in a Supercritical Carbon Dioxide Centrifugal Compressor at Low Flow Rate Conditions

With the advantages of high efficiency and compact structure,supercritical carbon dioxide(sC02)Brayton cycles have bright prospects for development in energy conversion field.As one of the core components of the power cycle,the centrifugal compressor tends to operate near the critical point(304.13 K,7.3773 MPa).Normally,the compressor efficiency increases as the inlet temperature decreases.When the inlet temperature is close to the critical point,the density increases sharply as the temperature decreases,which results in quickly decreasing of volume flow rate and efficiency reducing.The flow loss mechanism of the sCO_(2) compressor operating at low flow rate is studied in this paper.Computational fluid dynamics(CFD) simulations for sCO_(2)compressor were carried out at various inlet temperatures and various mass flow rates.When the sCO_(2)compressor operates at low volume flow rate,the flow loss is generated mainly on the suction side near the trailing edge of the blade.The flow loss is related to the counterclockwise vortexes generated on the suction side of the main blade.The vortexes are caused by the flow separation in the downstream region of the impeller passage,which is different from air compressors operating at low flow rates.The reason for this flow separation is that the effect of Coriolis force is especially severe for the sCO_(2) fluid,compared to the viscous force and inertial force.At lower flow rates,with the stronger effect of Coriolis force,the direction of relative flow velocity deviates from the direction of radius,resulting in its lower radial component.The lower radial relative flow velocity leads to severe flow separation on the suction side near the trailing edge of the main blade.

3-D NUMERICAL SIMULATIONS OF FLOW LOSS IN HELICAL CHANNEL

The flow loss of a helical channel Magnetohydrodynamic （MHD） thruster without MHD effect was numerically studied with 3-D simulations, and a flow loss coefficient （ was defined to quantify the flow loss and its influencing factors were studied. The results show that （ decreases in a first-order exponential manner with the pitch of a helical wall and the Reynolds number, and it declines slowly when t / T 〉 0.2 and Re 〉 10^5, a flow guide makes the flow more smooth and uniform, especially in the flow guide and helical wall sub-regions and thus reduces the flow loss greatly, by about 30% with the averaged value of （ from 0.0385 to 0.027, a rectifier weakens the helical flow and strengthens the axial one in the rectifier and outlet sub-regions, thus reduces the rotational kinetic pressure with the averaged value of ξ declining about 4% from 0.0385 to 0.037, and ξ decreases with a rectifier＇s axial length when Re 〉 10^5 .

Research on Flow Loss of Inlet Duct of Marine Waterjets

In the process of performance prediction of waterjet system,the flow loss of inlet duct is usually reckoned by the rule of thumb. But its value is often overestimated to some extent,resulting in error of prediction accuracy. This paper introduces a new method to determine the flow loss by means of computational fluid dynamic (CFD). Firstly,the fluid field around waterjet system is simulated by solving the Reynolds Averaged Navier-Stokes (RANS) equations using commercial CFD code Fluent. Then an additional User-Defined Scalar (UDS) equation is embedded into Fluent to get the virtual dividing surface between the internal flow ingested into the inlet duct and the external flow beneath the hull,which is named as streamtube. By virtual of the streamtube the flow loss can be calculated according to the difference of total pressure between the duct outlet and the capture area ahead of the intake. The results from CFD calculation show that the flow loss coeflcient of a typical flush-type inlet duct is varying from 0.05 to 0.12 at different operation conditions,being obviously less than the value of 0.2-0.3 from empirical rules. With the results of this paper the prediction accuracy on propulsive performance of the waterjet system can be improved further.

Tip-leakage flow loss reduction in a two-stage turbine using axisymmetric-casing contouring

In order to reduce the losses caused by tip-leakage flow, axisymmetric contouring is applied to the casing of a two-stage unshrouded high pressure turbine（HPT） of aero-engine in this paper. This investigation focuses on the effects of contoured axisymmetric-casing on the blade tipleakage flow. While the size of tip clearance remains the same as the original design, the rotor casing and the blade tip are obtained with the same contoured arc shape. Numerical calculation results show that a promotion of 0.14% to the overall efficiency is achieved. Detailed analysis indicates that it reduces the entropy generation rate caused by the complex vortex structure in the rotor tip region, especially in the tip-leakage vortex. The low velocity region in the leading edge（LE） part of the tip gap is enlarged and the pressure side/tip junction separation bubble extends much further away from the leading edge in the clearance. So the blocking effect of pressure side/tip junction separation bubble on clearance flow prevents more flow on the tip pressure side from leaking to the suction side, which results in weaker leakage vortex and less associated losses.

Experimental Studies on The Mechanism and Control of Secondary Flow Losses in Turbine Cascades

This paper summarizes the results of the authors' 4 year experimental studies on the secondary flow losses in turbine cascades.cascade wind tunnel experiments were carried out concerning the influence of aspect rations,incidence,turning angles and outer endwall divergent angles in order to unveil the evolution mechanism of secondary flow losses in turbine cascades without end clearance.Some methods for controlling the secondary flows are investigated including the blade leaning,blade cambering,endwall convergence and leading edge extension at two ends of the blade.

Profile and Secondary Flow Losses in a High-Lift LPT Blade Cascade at Different Reynolds Numbers under Steady and Unsteady Inflow Conditions

The aerodynamic flow field downstream of a Low-Pressure High-Lift(HL)turbine cascade has been experimentally investigated for different Reynolds numbers under both steady and unsteady inflows,in order to analyse the cascade performance under real engine operating conditions.The Reynolds number has been varied in the range 100000<Re<300000,where lower and upper limits are typical of cruise and take-off/landing conditions,respectively.The effects induced by the incoming wakes at the reduced frequency f+=0.62 on both profile and secondary flow losses have been investigated.Total pressure,velocity and secondary kinetic energy distributions at the downstream tangential plane have been measured by means of a miniaturized 5-hole probe.These quantities provide information on both blade wake and secondary flow structures(passage and horse-shoe vortices).The analysis of the results allows the evaluation of the aerodynamic performance of the HL front-loaded blade in terms of both profile and secondary losses.

Investigation of the Vortex Dynamic Mechanism of the Flow Losses on a Transonic Compressor Stator

For a transonic axial-flow compressor, the numerical simulations, verified against experimental data, were used to study the inherent correlation between the evolutionary process of the vortex structures and the flow loss in a compressor stator passage during the throttling process. The flow loss was divided accurately and quantitatively, based on the evolutionary process of the vortex structures. According to the position of the singular points of the vortex structures, the influence of the evolution of the vortex structures on the generation and development of the flow loss was analyzed on a microscale scale. Thereafter, this paper provided the vortex dynamic mechanism of the flow loss, which was important to enrich the theoretical system of the flow field in the compressor. The results show that: the flow loss at the top of the stator tip is caused by the low-energy fluid clusters, which are transported and accumulated by the vortices from the endwall; the transport effect of the pressure separation vortex at the upper half-height only migrates the position of the flow losses, but there is new flow loss generated by its shear action to the endwall. The dominant flow loss during the throttling process concentrates upon the closed separation bubble around the middle of the suction side of the stator.

THE LOSS OF STABILITY OF LAMINAR FLOW IN OPEN CHANNEL AND THE MECHANISM OF SAND RIPPLE FORMATION

In the flow on a mobile bed in an open channel, sand ripple often appears after the sediment begins to move. Different scholars have different views on the formation of sand ripples. This paper holds that as the ripple in general is very small, its formation is due to the instability of the laminar flow or the evolution of the small-scale coherent structures in the sublayer adjacent to the wall of the open channel. When the shear stresses caused by the disturbing waves or the coherent structure near the bed surface boundary and the water flow itself are greater than the shields stresses, responses on the bed surface appear and the sand ripple forms. If the frequency of the shear stress caused by the disturbance is close to the natural frequency of the sand grains that produced resonance, such a phenomenon is called the 'detection property' of the sediment. It is at this point that the maximum resonance appears and the sand ripple develops rapidly.

COMPUTATIONAL FLUID DYNAMICS RESEARCH ON PRESSURE LOSS OF CROSS-FLOW PERFORATED MUFFLER

The pressure loss of cross-flow perforated of physical modeling, simulation and data processing. muffler has been computed with the procedure Three-dimensional computational fluid dynamics （CFD） has been used to investigate the relations of porosities, flow velocity and diameter of the holes with the pressure loss. Accordingly, some preliminary results have been obtained that pressure loss increases with porosity descent as nearly a hyperbolic trend, rising flow velocity of the input makes the pressure loss increasing with parabola trend, diameter of holes affects little about pressure loss of the muffler. Otherwise, the holes on the perforated pipes make the air flow gently and meanly, which decreases the air impact to the wall and pipes in the muffler. A practical perforated muffler is used to illustrate the available of this method for pressure loss computation, and the comparison shows that the computation results with the method of CFD has reference value for muffler design.

Debris Flows Risk Analysis and Direct Loss Estimation:the Case Study of Valtellina di Tirano,Italy

Landslide risk analysis is one of the primary studies providing essential instructions to the subsequent risk management process. The quantification of tangible and intangible potential losses is a critical step because it provides essential data upon which judgments can be made and policy can be formulated. This study aims at quantifying direct economic losses from debris flows at a medium scale in the study area in Italian Central Alps. Available hazard maps were the main inputs of this study. These maps were overlaid with information concerning elements at risk and their economic value. Then, a combination of both market and construction values was used to obtain estimates of future economic losses. As a result, two direct economic risk maps were prepared together with risk curves, useful to summarize expected monetary damage against the respective hazard probability. Afterwards, a qualitative risk map derived using a risk matrix officially provided by the set of laws issued by the regional government, was prepared. The results delimit areas of high economic as well as strategic importance which might be affected by debris flows in the future. Aside from limitations and inaccuracies inherently included in risk analysis process, identification of high risk areas allows local authorities to focus their attention on the "hot-spots", where important consequences may arise and local(large) scale analysis needs to be performed with more precise cost-effectiveness ratio. The risk maps can be also used by the local authorities to increase population's adaptive capacity in the disaster prevention process.

Characteristics of runoff processes and nitrogen loss via surface flow and interflow from weathered granite slopes of Southeast China

Rainfall intensity and slope gradient are two of the most important factors affecting the variations of runoff nitrogen(N).However,the effects of slope gradient and rainfall intensity on N loss via surface flow and interflow on weathered granite slopes are poorly understood.In this study,12 artificial rainfalls(three rainfall intensities and four slope gradients)were simulated to investigate the coupling loss characteristics of surface flow–interflow–total nitrogen(TN),nitrate nitrogen(NO_3^--N)and ammonia nitrogen(NH_4^+-N)on weathered granite slopes.The results show that slope gradient has a greater impact on the surface flow when the rainfall intensity is relatively large.The effect gradually weakens with the decrement of rainfall intensity.The interflow yield increases firstly with the prolongation of rainfall duration,then tends to be stable and finally decreases.The total surface flow percentage increases with rainfall intensity while it decreases with increasing slope gradient with a range of 10.88%-71.47%.The TN loss concentration of the surface flow continually decreases with rainfall duration while that of the interflow shows different fluctuations.However,the TN loss loads of both surface flow and interflow increase with increasing rainfall intensity and slope gradient.The NO_3^--N concentration of interflow is much higher than that of the surface flow.The NH_4^+-N concentration is always less than that of NO_3^--N with no significant difference between surface flow and interflow.The percentages of the TN,NO_3^--N,and NH_4^+-N total loss load and concentration of surface flow and interflow were analyzed.The results show that N loss via both surface flow and interflow occurs mainly in the form of NO_3^--N.Most of the N loss is caused by interflow which is the preferential path of runoff nutrient loss.These findings provide data support and underlying insights for the control of runoff and N loss on the weathered granite slopes.

Investigating the Effects of Slack Bus Selection in Load Flow Studies: A Comparative Analysis of Robust and Weak Grids

Load flow studies play a critical role in the analysis of power systems. They enable the computation of voltage, current, and power flows in a power system. They provide valuable insights into the steady-state performance of the power system under different operating conditions. Choosing a slack bus is a vital step in conducting load flow simulations. A slack bus is a PV bus that includes a generator and is used to balance real and reactive power during load flow studies. Many studies have been conducted on the selection of slack buses in load flow analysis. However, varied conclusions regarding the impact on system losses and power flows were obtained during these studies. Therefore, using the IEEE-14 bus test system, this study investigated the effects of slack bus selection in strong and weak grids by alternating slack buses among PV buses and observing the effects on bus voltage magnitude, bus voltage phase angle, total power flows, and active and reactive power losses. The study noted that the effect of slack bus selection on these system quantities is contingent upon the voltage stability of the grid. Whereas in a robust grid, system losses and power flows remained constant irrespective of the choice of slack bus, a weak grid experienced some variations in these system quantities under similar circumstances. The simulation results led to the conclusion that, to a large extent, the voltage stability of the grid plays a significant role in determining the degree to which slack bus selection affects system losses and other quantities in load flow studies.

Analysis of the Pipe Heat Loss of the Water Flow Calorimetry System in EAST Neutral Beam Injector

Neutral beam injection heating is one of the main auxiliary heating methods in controllable nuclear fusion research. In the EAST neutral beam injector, a water flow calorimetry （WFC） system is applied to measure the heat load on the electrode system of the ion source and the heat loading components of the beamline. Due to the heat loss in the return water pipe, there are some measuring errors for the current WFC system. In this paper, the errors were measured experimentally and analyzed theoretically, which lay a basis for the exact calculation of beam power deposition distribution and neutralization efficiency.

基于产量损失率的气井合理配产方法研究

合理配产对气井生产具有非常重要的作用。现有的配产方法一般是按照无阻流量的1/6∼1/3来进行。在研究气体在地层中的非达西效应的基础上,提出了产量损失率的概念,通过量化非达西效应造成的产量损失,建立了气井产量损失率与无因次产量的图版。对于每一个配产,可得到与其相应的产量损失率,非达西效应对气井产量的影响就有了定量化的表征。因此,可根据产量损失率来进行合理配产。对于某些高压气藏,由于地层压力高,气体压缩程度大,地层条件下非达西效应并不强,产量损失率比较低,这类气井就可以将产量配高一些。该配产方法可实现量化储层气体非达西渗流损失,实现气井合理配产。该研究成果能在气井常规配产方法的基础上,进一步优化气井配产制度,更好地满足气井长期稳产、高效开发的需求,为气藏开发提供有益的借鉴。

震后RC桥墩竖向承载力最优工程需求参数的选取方法

桥墩结构的震后竖向承载力是评估梁式桥梁震后通行功能的重要指标,但其难以测量。为了快速定量地评估桥梁结构的震后通行能力,对评估梁式桥梁结构震后竖向承载力的最优工程需求参数(EDP)进行了系统地研究。首先选取与墩柱残余侧移和损伤相关的5个EDPs,通过对考虑了材料不确定性的RC桥墩进行Pushover分析和动力时程分析得到5个EDPs,进一步对震后的桥墩进行Pushdown分析获取震后竖向承载力。然后采用回归模型对所选EDPs与震后竖向承载力损失比的关系曲线进行回归分析,选取竖向承载力损失比关系曲线的最优回归模型为在ln(x)-y坐标系中的正态累积函数模型,进一步通过最优EDP评价准则对评估竖向承载力损失比的5个EDPs进行评价分析。评价结果表明:当考虑震后可计算性时,峰值侧移率最优;当考虑震后可测性时,残余侧移率最优;当考虑余震时,改进的Park-Ang指标最优。通过选取的最优EDP可以建立桥梁结构功能指标与抗震性能指标之间的联系,为进一步发展和完善桥梁结构的抗震韧性评估和设计提供参考。

不同编织方式下陶瓷基复合材料表面流动特性数值计算研究

Ceramic matrix composites(CMCs) are one of the most promising materials in the field of gas turbines,with superior weight and thermal properties. Its surface morphology is different from the traditional casting airfoil components, which mainly comes from different weaving methods and different braided tow thickness. However, few people have studied the influence of surface morphology of ceramic matrix composites(CMCs) on the development of boundary layer and the resulting flow loss. In this paper, Tex Gen is used to generate different surface morphology structures of ceramic matrix composites(CMCs), and the surface flow characteristics of corresponding CMCs plates are numerically studied. It is found that the slope of the displacement thickness of the woven surface first increases and then decreases in the whole transition interval. Thicker braided tow thickness and denser braiding method will induce earlier flow transition phenomenon and produce greater flow loss;The flow loss on the surface of CMCs plate is mainly composed of the vortex loss in the pit and the boundary layer loss outside the pit, and the boundary layer loss is dominant. The weaving methods has a greater influence on the flow state and flow loss of the boundary layer.

不同缩口下闸阀介质流动特性研究

阀门的缩口比是阀门使用单位及生产单位关注的重要因素,直接关系到机组运行性能参数。文中分别以DN100和DN350闸阀,以缩口比0.75、0.8、0.85、0.90、0.95及1.0建立三维模型,并利用FLUENT软件进行流场模拟分析,模拟不同缩口的闸阀内介质的流动状态,获取其速度场和压力场,并计算出不同缩口下阀门的流阻系数。根据流阻系数计算出工况参数下阀门压力损失,为阀门使用单位及生产制造单位提供选型参考方案。

基于场景流的可变速率动态点云压缩

针对现有的动态点云压缩神经网络需要训练多个网络模型的问题,提出基于场景流的可变速率动态点云压缩网络框架.网络以原始动态点云为输入,利用场景流网络进行运动向量估计,在压缩运动向量和残差的同时,引入通道增益模块对隐向量通道进行评估和缩放,实现可变速率控制.通过综合考虑运动向量损失和率失真损失,设计新的联合训练损失函数,用来端到端地训练整个网络框架.为了解决动态点云数据集缺少真实运动信息标签的问题,基于AMASS数据集制作带有运动向量标签的人体数据集,用于网络的训练.实验结果显示,与现有的基于深度学习动态点云压缩方法相比,该方法的压缩比特率下降了几个数量级,与静态压缩网络单独处理每帧的重构效果相比,该方法有5%~10%的提升.