新型流速传感器及其流速数据采集系统

新型流速传感器采用红外调制电路以克服环境光对流速测量的影响 ,流速数据采集系统采用工业化脉冲计数模块 .因此 ,该系统具有较好的稳定性和可靠性 ,且成本低 ,配置方便 .

ADCP流速数据综合滤波算法研究

针对现有ADCP流速数据滤波方法单一导致滤波效果不佳的缺陷,在分析ADCP观测误差来源的基础上,基于对几种流速滤波方法的特点的总结分析,给出了一种ADCP数据综合滤波方法,即首先设计自适应窗口,利用中值滤波对原始流速数据进行异常值剔除得到初步结果,继而分析初步结果的功率谱图,设计DFT滤波器;对初步结果进行窗函数法滤波,以获得最佳滤波效果。实验结果表明,综合滤波法对白噪声(随机误差)滤除效果较好,特别是对存在少量连续、非连续异常值的流速数据,其滤波结果优于传统滤波方法。

基于三维相空间法和稳健估算法的ADV流速数据后置处理效果研究

水流是影响藤壶、牡蛎、藻类等水生生物能否成功附着在渔业装备上的重要环境因素,水体流速的变化会改变藻类新陈代谢过程,制约藤壶与牡蛎幼虫大面积扩散。流速测量数据的准确性对研究渔业装备上附着生物的附着机制起到至关重要的作用。声学多普勒流速仪(ADV)是测量水体流速的重要设备。然而,水体中的气泡、大颗粒悬浮物等因素会影响ADV的相关系数和信噪比,从而导致流速数据中产生野点,降低了数据的准确性。本文基于国内外主流算法稳健估算法与三维相空间法,以ADV实际测量的流速数据为例,对比研究两种后置处理方法的检测效果。结果显示,稳健估算法平均检出率为4.95%,峰度系数平均下降77.71%,三维相空间法平均检出率为14.60%,峰度系数平均下降84.05%。综合分析,三维相空间法处理效果较好,其检测准确性高于稳健估算法,但存在过处理现象。建议在处理野点含量低于5%的数据时选用相空间法,而对于野点偏离样本平均值较远的数据时,可以选用稳健估算法。本文对减小流速数据误差,为准确定量研究水流对渔业装备附着生物的附着量与种类影响有着重要的意义。

流速仪信号采集系统设计

介绍了流速仪检定系统的工作原理,分析流速仪信号特点和采集难点,针对流速仪信号受外界干扰信号波形复杂问题,设计信号采集硬件调理电路。针对流速仪信号周期多样性问题,对测频法和测周法进行误差分析和比较,确定在不同速度区间使用不同软件滤波的方法。通过硬件调理电路及软件滤波仿真验证,证明设计的可行性,可有效提高流速仪信号采集的精度,并在单片机平台上完成了硬件设计。

大数据:改变游戏规则的技术

大数据既让人头疼,又是一大机遇。在数据处理方面,各机构都处在转折点上,开展业务也变得困难。如果不加以改变,数据会把你淹没,成为基础设施的沉重开支和风险负担。但如果你知道如何利用它,它就会变成一个资本。

Bed Load Transport Rates during Scouring and Armoring Processes

Dambreak-induced bed scouring may undermine the foundation of bridge piers and other structures,and that destruction can pose a serious threat.Consequently,this paper aims at exploring the mechanisms of scouring and armoring.Firstly,the incipient velocity for nonuniform sediment particles was studied,and a formula was derived based on the angle of repose of nonuniform sediment.The results showed that the mechanism of incipient motion for sand and fine gravel differed from that for coarse gravel and cobbles.Also,comparison between experimental and field data shows that the results from the proposed formula agree well with those observed for all conditions.Secondly,a birth-death,immigration-emigration Markov process was developed to describe the bed load transport rate associated with scouring and armoring.The comparison between experimental data and computed results shows that our model can predict the bed load transport rate,although there may be some limitations,the chief of which is that there are many variables in the model to be determined through experiment.This makes its application in river engineering inconvenient.

Model for seawater fouling and effects of temperature,flow velocity and surface free energy on seawater fouling

A kinetic model was proposed to predict the seawater fouling process in the seawater heat exchangers.The new model adopted an expression combining depositional and removal behaviors for seawater fouling based on the Kern–Seaton model.The present model parameters include the integrated kinetic rate of deposition(k d)and the integrated kinetic rate of removal(k r),which have clear physical signi ficance.A seawater-fouling monitoring device was established to validate the model.The experimental data were well fitted to the model,and the parameters were obtained in different conditions.SEM and EDX analyses were performed after the experiments,and the results show that the main components of seawater fouling are magnesium hydroxide and aluminum hydroxide.The effects of surface temperature,flow velocity and surface free energy were assessed by the model and the experimental data.The results indicate that the seawater fouling becomes aggravated as the surface temperature increased in a certain range,and the seawater fouling resistance reduced as the flow velocity of seawater increased.Furthermore,the effect of the surface free energy of metals was analyzed,showing that the lower surface free energy mitigates the seawater fouling accumulation.

Highly nonlinear internal solitary waves over the continental shelf of the northwestern South China Sea

Large amplitude internal solitary waves(ISWs) often exhibit highly nonlinear effects and may contribute significantly to mixing and energy transporting in the ocean.We observed highly nonlinear ISWs over the continental shelf of the northwestern South China Sea(19°35'N,112°E) in May 2005 during the Wenchang Internal Wave Experiment using in-situ time series data from an array of temperature and salinity sensors,and an acoustic Doppler current profiler(ADCP).We summarized the characteristics of the ISWs and compared them with those of existing internal wave theories.Particular attention has been paid to characterizing solitons in terms of the relationship between shape and amplitude-width.Comparison between theoretical prediction and observation results shows that the high nonlinearity of these waves is better represented by the second-order extended Korteweg-de Vries(KdV) theory than the first-order KdV model.These results indicate that the northwestern South China Sea(SCS) is rich in highly nonlinear ISWs that are an indispensable part of the energy budget of the internal waves in the northern South China Sea.

Research on characteristics of water motion and influencing factors for the flexible air chamber jig body

The air bag deformation data were obtained by high-speed dynamic videos experiments. Based on gas–liquid flow VOF model, dynamic mesh technique and deformation data, numerical simulations for different structure models were achieved, and the law of water motion and influencing factors were analyzed.The results show that the flow in the length direction of the jig is smooth, and second pulsation appears in the separation time and forms the secondary separation. The installation position of screen and the number of air bags have a great influence on the uniformity of flow and velocity. The screen height cannot be too low to avoid forming the unstable flow. At the same time, the screen height cannot be too high, otherwise water velocity will be too small and was unable to provide enough power. At the height of 1.4m,velocity unevenness is minimum and the best uniform flow can be obtained. Compared with double air bags, there are the following features of single air bag: water flow is not smooth, the time achieving the maximum velocity is too long, maximum velocity is smaller, and overall effect is worse than double air bags.

Bottleneck Analysis for Data Acquisition in High-Speed Network Traffic Monitoring

The increasing network throughput challenges the current network traffic monitor systems to have compatible high-performance data processing.The design of packet processing systems is guided by the requirements of high packet processing throughput.In this paper,we depict an in-depth research on the related techniques and an implementation of a high-performance data acquisition mechanism.Through the bottleneck analysis with the aid of queuing network model,several performance optimising methods,such as service rate increasing,queue removing and model simplification,are integrated.The experiment results indicate that this approach is capable of reducing the CPU utilization ratio while improving the efficiency of data acquisition in high-speed networks.

Evaluation of Program Code Caching for Mobile Agent Migrations

Mobile agents are able to migrate among machines to achieve their tasks. This feature is attractive to design, implement, and maintain distributed systems because we can implement both client-side and server-side programming in one mobile agent. However, it involves the increase of data traffic for mobile agent migrations. In this paper, we propose program code caching to reduce the data traffic caused by mobile agent migrations. A mobile agent consists of many program codes that define a task executed in each machine they migrate; thus, the mobile agent migration involves the transfer of their program codes. Therefore, our method reduces the number of the transfer of program codes by using program code cache. We have implemented our method on a mobile agent framework called Maglog and conducted experiments on a meeting scheduling system.

Application of Rainbow Schlieren Deflectometry for Axisymmetric Supersonic Jets (Comparison of Experiments with Numerical Analysis)

This paper analyzes the correctly-expanded supersonic jet from a convergent-divergent axisymmetric nozzle by using numerical simulation of turbulent flow.And the calculated density distributions in this flow are compared with the present experimental data using rainbow schlieren deflectometry.The value of the density from the experimental data agrees well with the results calculated by this simulation.Therefore,the present method of the measurement using rainbow schlieren deflectometry is useful for the measurement of the density of the correctly-expanded supersonic jet.

Effect of Nonequilibrium Homogenous Condensation on Flow Fields in a Supersonic Nozzle

When condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, a condensing flow was produced by an expansion of moist air in a supersonic circular nozzle, and, by inserting a wedge-type shock generator placed in the supersonic part of the nozzle, the experimental investigations were carried out to clarify the effect of condensation on the normal shock wave and the boundary layer. As a result, the position of the shock wave relative to the condensation zone was discussed, together with the effect of condensation on pressure fiuctuations. Furthermore, a compressible viscous two-phase flow of moist air in a supersonic half nozzle was calculated to investigate the effect of condensation on boundary layer.

A Study on High Subsonic Airfoil Flows in Relatively High Reynolds Number by Using OpenFOAM

In the present study,numerical calculations of the flow-field around the airfoil model are performed by using the OpenFOAM in high subsonic flows.The airfoil model is NACA 64A010.The maximum thickness is 10 % of the chord length.The SonicFOAM and the RhoCentralFOAM are selected as the solver in high subsonic flows.The grid point is 158,000 and the Mach numbers are 0.277 and 0.569 respectively.The CFD data are compared with the experimental data performed by the cryogenic wind tunnel in the past.The results are as follows.The numerical results of the pressure coefficient distribution on the model surface calculated by the SonicFOAM solver showed good agreement with the experimental data measured by the cryogenic wind tunnel.And the data calculated by the SonicFOAM have the capability for the quantitative comparison of the experimental data at low angle of attack.

Progress in research on mixing techniques for transverse injection flow fields in supersonic crossflows

The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are pro- posed, especiaUy data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.