PROPER ORTHOGONAL DECOMPOSITION AND LOW-DIMENSIONAL APPROXIMATION OF WALL PRESSURE FLUCTUATION

Wall pressure fluctuation is one of the source terms which result in the vibration of hydraulic structures. To consider both the space and time correlation of the pressure field, the method of proper orthogonal decomposition and lowdimensional approximation were used here to describe the pressure signals of the turbulent boundary layer, the apron of the stilling pond and the vertically impinging jet.     

STUDIES ON STATISTICAL CHARACTERISTICS OF THE PRESSURE FLUCTUATION AMPLITUDE IN OUTLET WORKS

The pressure fluctuation amplitude is very important for the load design of structures and to research flow cavitation, using 182 sample records of fluctuation pressure obtained from model tests and prototype observations for many kinds of outlet works,this paper studies statistical characteristics of fluctuating pressure amplitude in outlet works. The results indicate that the probability of fluctuating pressure amplitude in outlet works obeys Gaussian normal distribution,and the verification of prototype observation data from Gezhouba project further proves that the conclusion is true.     

APPLICATION OF LYAPUNOV EXPONENT SPECTRUM IN PRESSURE FLUCTUATION OF DRAFT TUBE

The Lyapunov exponent spectrum is firstly applied in the analysis of pressure fluctuation of draft tube and calculated based on the time series of vibration in experiments for different situations. Results shows that the Lyapunov exponent spectrum varies with the setting of guide vane, So the Lyapunov exponent spectrum can be used to judge the pressure fluctuation of draft tube so as to timely adjust the setting of the guide vanes to reduce the damage caused by the vibration.     

液压抓斗造塑性砼防渗墙在大坝除险加固中的应用

以黄金水库大坝除险加固工程为实例,介绍了液压抓斗造塑性砼防渗墙在土坝加固中的应用.     

太平湾大坝扬压力超限原因及对坝体稳定影响

对于坝高较小的混凝土重力坝 ,扬压力对坝体稳定影响极大。通过对太平湾大坝扬压力超限原因的分析 ,研究了影响扬压力的因素 (坝体温度、坝体地质条件、坝体结构、基础防渗帷幕及固结灌浆、坝体排水等 )。文章并提出了降低扬压力的措施。     

WALL PRESSURE FLUCTUATIONS OF TURBULENT FLOW OVER BACKWARD-FACING STEP WITH AND WITHOUT ENTRAINMENT： MICROPHONE ARRAY MEASUREMENT

1. INTRODUCTION Turbulent boundary layer flows over surface irregularity are of significant importance from both fundamental and practical essences. Among others, turbulent flows over backward-facing step (hereinafter referred to BFS) received widespread …     

EXPERIMENTAL STUDY ON THE SECOND-ORDER DIFFRACTION WAVE PRESSURE AND FORCE ON A CIRCULAR CYLINDER UNDER STOKES WAVE ACTION

This paper presents the model test to measure the second-order wave pressureand forces on a circular cylinder fixed in Stokes wave with a given draught.The distributions ofsecond-order oscillating and steady wave pressure on the wet surface of the cylinder and secondorder oscillating wave forces were obtained in this test,but the second-order steady wave forcewas not able to be measured due to its very small magnitude.The test results also show thatthird-order wave force may be greater than the second-order force when wave frequencies arehigh.The experimental results were compared with the corresponding calculation results of Ref-erence[3].     

NUMERICAL SIMULATION OF AN OSCILLATING FLOW PAST A CIRCULAR CYLINDER IN THE VICINITY OF A PLANE WALL

Oscillating flow around a circular cylinder in the vicinity of a plane wall was investigated by solving the two-dimensional incompressible Navier-Stokes equations with a finite element Galarkin residual method. The effect of the gap G/D between the cylinder surface and the wall on the flow behavior was studied. For the case of G/D 〈 0.25, the periodicity in the flow is attributed to both the outer shear layer instability and the oscillating frequency. As G/D 〉 0.25, vortex shedding occurs and the periodicity in the flow is mainly due to the competition of the oscillating frcqucncy and the vortex shedding frequency from an isolated stationary cylinder.     

MODEL OF SEA ICE BREAKUP ON SHALLOW BEACH DUE TO TIDAL FLUCTUATION

1.　 INTRODUCTIONThe breakup ofice isthe basis to analyze the mechanism of ice ride-up and pile-up,andto further study the formation of rafted ice and ice ridge.Up till now,researcheshave focused on the effectof wind and currenton shore fasticebreakup.Christensen F.T.[1 ] analyzed the possible size ofthe ice pieces when the ice floe in-teracts with the slope underthe action of wind and currentdriving forces.S rensen C.[3] in-vestigated the failure of a floating ice floe when itcollided w…     

THE FLUCTUATION CHARACTERISTICS OF NATURAL AND VENTILATED CAVITIES ON AN AXISYMMETRIC BODY

Natural and ventilated cavitations generated on a smooth-nosed axisymmetric body were studied experimentally. The characteristics of small scale and localized fluctuations of “steady cavities” were measured by pressure transducers. Comparisons between natural and ventilated cavities at different measured points for several cavitation numbers were done. It was observed that the dominant fluctuations were concen trated in the frequency range of 0Hz 50Hz for all the cavitation cases, Similar shapes and magnitudes of the frequency spectra were detected for both natural and ventilated cavities.Much larger spectral amplitude in the cavity closure region suggested as fluctuations source. From partial cavitating flow to supercavitating flow, the dominant frequency and the corre sponding amplitude decreased with decreasing cavitation number, which meant that cavity became more steady while developing.     

光电式垂线坐标仪与引张线仪的工程应用

简要介绍了新型光电式垂线坐标仪与引张线仪的原理、结构和技术特点。通过在小东江水电站坝顶位移自动化观测的实际应用，表明系统稳定性好、可靠性强，在大坝安全监测中具有较好的应用价值。     

SMW工法围护结构的设计

根据SMW工法的用途和特点,提出了该方法在围护工程中的设计计算理论和设计准则,总结出SMW工法的特点和优势,以便在今后的工程实践中更好的加以运用。     

SCALE EFFECT OF IMPINGING PRESSURE CAUSED BY SUBMERGED JET

The characteristics of the impinging pressure at the jet equipment where the maximum jet velocity can reach 50m/s were studied. By comparing the impinging pressure with the one measured at the low velocity conditions, two conclusions of the scale effect are drawn： firstly, the velocity attenuation degree is smaller than that of low velocity jet, and secondly, the relative impinging width is narrower than that of low-velocity jet. The reasons of the scale effect of the impinging pressure were elucidated through numerical simulation.     

CHARACTERISTICS OF CORRELATION AND SPECTRUM BETWEEN WALL FLUCTUATING PRESSURE AND FLUCTUATING VELOCITY OF IMPINGING JET

The correlation, the spectrum and the turbu-lent scale between wall fluctuating pressure and fluctuating ve-locity, on the bed of plunging pool under the action of single and twin impinging jet, are investigated in the paper by using 2-D LDA and the dynamic pressure scanning system of multi-ple points. It is found that the cross correlation between the horizontal fluctuating velocity and the fluctuating pressure of twin jet is bigger than that of sinlge jet, and the spectrum be-tween horizontal fluctuating velocity and fluctuating pressure obviously has approximately dominant frequency. The rela-tionship between the fluctuation pressure coefficient on wall and the turbulent intensity near the wall can be described with logarithmic curve.     

VORTEX SHEDDING FREQUENCY DETERMINED BY SURFACE PRESSURE FLUCTUATIONS OF THREE EQUISPACED CYLINDERS

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HYDRAULIC PRESSURE SIGNAL DENOISING USING THRESHOLD SELF-LEARNING WAVELET ALGORITHM

A pre-filter combined with threshold self-learning wavelet algorithm is proposed for hydraulic pressure signals denoising. The denoising threshold is self-learnt in the steady flow state, and then modified under a given limit to make the mean square errors between reconstruction signals and desirable outputs minimum, so the corresponding optimal denoising threshold in a single operating case can be obtained. These optimal thresholds are used for the whole signal denoising and are different in various cases. Simulation results and comparative studies show that the present approach has an obvious effect of noise suppression and is superior to those of traditional wavelet algorithms and back-propagation neural networks. It also provides the precise data for the next step of pipeline leak detection using transient technique.     

EFFECT OF AERATOR ON HYDRAULIC DRAG ACTING ON A CHUTE

The formulae used to calculate the friction in the non-uniform flow chute were examined with the experimental data. and the results show that the accuracy of the formula is enough for engineering applications. A comparison between the results of friction respectively from the uniform flow assumption and the non-uniform flow approximation indicates that the former is an order of magnitude larger than the latter in the case of steep chute. The hydr~3ulic drag on a steep chute with aerators was measured on the hydraulic model directly and the coefficient of the aerator effect on the drag was obtained. The variation patterns of the wall shear just down stream of the aerators were investigated and the mechanism of the increase in the drag by aerator were analyzed qualitatively with the measured water depths just downstream the aerators.     

THE STATISTICAL DISTRIBUTION OF EXTREME VALUES OF WAVE-CURRENT FORCES ACTING ON SLENDER CIRCULAR CYLINDER IN IRREGULAR WAVES

Based on model test,the statistical distribution of extreme values of wave-current in-line forces acting on vertical circular cylinder is analyzed in this paper.It is shownthat the results calculated by the simplified method,proposed by authors,agree well with the testdata;Weibull distribution is also adoptable in the region of high KC number, and the shapeparameter a and scale parameter β are related well with KC number respectively.     

MEASUREMENT OF HYDRODYNAMIC FORCES ACTING ON A CIRCULAR CYLINDER NEAR A PLANE BOUNDARY IN STEADY FLOW

In this paper,the characteristics of hydrodyna(?) forces on a circular cylindernear a plane boundary have been studied experimentally in w(?) tunnels.The drag coefficientC_D,mean lift coefficient C_(L0),T.m.s.lift coefficient C_(L Tms),maximum lift coefficient C_(L max) andfluctuating lift coefficients C'_(L Tms),C'_(L max),and lift(vortex shedding)frequency have been mea-sured on condition that the thickness of plane boundary layer,δ,was 0.1D(D is the diameter ofthe cylinder)at the station of the centre of the cylinder,and Reynolds number,Re,varied from4.5×10~3 to 1.76×10~5.The regularity of the change of these coefficients with Re and gap ratioG/D is found.The measurement of the lift frequency shows that a strong non-linear coupling ac-tion appears when the gap ratio between the circular cylinder and plane,G/D,reaches 0.5,andthe shedding of regular vortex is suppressed when G/D=0.2.     

一种软基挡土墙的基础处理办法

详细介绍了一种挡土墙的基础在软基上的处理措施,同时通过对桩的受力和位移分析,验证了该处理方法的可行性.经多年运行观测,结构安全可靠,无明显位移.