MATHEMATICAL MODELING OF OIL SPILL ON THE SEA AND APPLICATION OF THE MODELING IN DAYA BAY

Through the study of the theory of oil spill model, a mathematical modeling of oil spill on the sea is developed which with the consideration of spread, diffusion, drifting and attenuation of oil slick is influenced by evaporation and emulsification factors. A model that under the effect of ocean dynamic condition of tide, wind and wave, using Monte Carlo method to simulate the movement of oil slick is established. The modeling is applied to calculate and predict pollution range of oil spill at oil quay and oil ship in Daya Bay. The prediction results have basically shown the pollution situation by emergency of oil spill on the sea.     

Impact of light regimen and self-shading by algal cells on primary productivity in the water column of a shallow tropical lake (Lake Naivasha, Kenya)

Light is the factor that fundamentally determines the level of primary production. Primary productivity is controlled by bottom‐up factors (nutrient levels), with secondary effects due to biological factors (zooplankton grazing). The light regimen experienced by algae is determined largely by mixing of the water column. The processes of photoinhibition and light attenuation combine with the resultant light–dark adaptation to shape the vertical productivity profile and it is important to determine their importance separately because they vary spatially and temporally. Daily variations in productivity can be as large as longer‐term changes and events causing high productivity may not be important in whole‐lake terms. At approximately 0.5 m depth, there is maximal photosynthesis causing depletion of nutrients, but there is vertical homogeneity in productivity control and horizontal similarity in productivity levels. There is zero productivity below 5 m depth due to light attenuation but, if the benthos becomes productive due to an environmental change, such as decreased turbidity, overall productivity may rise appreciably. Self‐shading was investigated by incubating serial dilutions of whole lakewater with filtered water to reduce the density of algal cells. Photosynthetic efficiency was calculated as productivity per unit of chlorophyll a. Self‐shading showed different responses for conditions of ‘low’ and ‘high’ productivity. With low productivity, there was a shading loss of 17%, while for high productivity this was 46%. Thus, self‐shading is seen to have a considerable impact on potential productivity and may affect phytoplankton–cyanobacterial community structure with implications for lake management.     

三峡库区典型支流水质模型及其参数敏感性分析

参数敏感性分析旨在确定水质模型中各参数对模型精度的影响,在利用水质模型分析时,可根据参数的敏感性精简模型中的大量参数。以三峡库区支流草堂河为例,建立相应生态动力学模型,并对模型结果进行验证,再进一步采用扰动分析法对模型中26个参数的敏感性进行了计算分析。研究结果表明:生化参数中浮游植物的最大生长率(R0)、适应温度下限(T1)、死亡线性系数(RDIE1)、光照最低值(IOPT)、消光系数(KC)、遮光系数(KW)及磷酸盐半饱和系数(KPO4)是敏感性最高的参数,其他参数敏感性相对较低;对同一参数而言,其敏感性亦会随季节改变发生变化,其敏感性一般在冬春季较低,夏秋季较高。     

CHARACTERISTIC ANALYSIS OF THE PLUNGING OF TURBIDITY CURRENTS

Turbidity currents are flows driven by suspended sediment of flood-induced turbid river water with excess density. Such currents are often the governing factor in reservoir sedimentation by transporting fine materials over long distances and delivering the majority of deposition, which thus reduces the storage capacity. Therefore, the design and operation of a reservoir requires an accurate prediction of its occurrence condition and plunging position, which is the objective of the present study. This article presents a verified algebraic slip mixture model including momentum, continuity and algebraic velocity expressions to simulate 2-D turbidity currents. Test experiments in a multiphase flume were carried out. Reynolds number, sediment concentration and densimetric Froude number were used as parameters in the occurrence condition analysis. The plunging of turbidity currents may produce reflux and backflow due to the diving flow at the surface of the clear water. The similar experimental results were also obtained by PIV measurements     

EXPERIMENTAL STUDY OF VELOCITY DISTRIBUTIONS IN THE TRANSITION REGION OF PIPES

The accuracy of an ultrasonic flowmeter meaurement depends on the profile-linear average velocity.But this velocity in the transition region is not available at the present.In this article,the velocity in the transition region in pipes is studied by experimental methods.The Particle Image Velocimetry (PIV) is used to measure the flow field in the transition region in pipes,and the measured results from PIV are in good agreement with the Westerwell’s experimental data.Based on the experimental data of PIV,the curves of the profile-linear average velocity in the transition region against the Reynolds number in the range from 2 000 to 20 000 are obtained,and it is shown that the coefficient k is constant when the Reynolds number is in the range of 2 000-2 400 and 6 000-20 000,and the coefficient k is increasing when the Reynolds number is in the range of 2 400-6 000.The results of this article can be used to improve the measurement accuracy of the ultrasonic flowmeters and as a theoretical basis for the research on the transition flow.     

PIV MEASUREMENT OF THE GAS-SOLID FLOW PATTERN IN A CFB RISER

Particle Imaging Velocimetry (PIV) is a valuable measuring tool for studying multiphase flows, such as liquid-gas and gas-solid flow. It can be used to carry out many hydrodynamic studies, in particular, to determine accurately the gas-solid flow structure in CFB (Circulating Fluidized Beds). In this paper, the technique characteristics was described in applying the PIV to measure the gas-solid flow in circulating fluidized beds. A primary experiment was completed on a CFB unit with the PIV, yielding the velocity vector fields of high-density particles for different gas-solid superficial velocities and solid recycle rates. Velocities of the transported particles were calculated with cross-correlation method. The major factors influencing the successful measurement of particle velocity with the PIV technique were also described.     

PIV algorithms for open-channel turbulence research: Accuracy, resolution and limitations

The implementation of PIV for experimental studies in open-channel flows can be challenging due to the presence of strong velocity gradients and the inclusion of solid interfaces in the captured images. Understanding the performance and limitations of the PIV method under these conditions is critical for optimising experimental parameters and robust interpretation of data. The optimum algorithm for extracting velocity fields from PIV images is the subject of ongoing revision with the goal of maximising resolution and minimising errors, and recent advances in this regard may be particularly beneficial for open-channel turbulence research. Key steps in the iterative discrete shift (IDS) and image deformation method (IDM) algorithms are detailed, and the fundamental differences between direct cross correlation and FFT-based correlation methods are explained. It is also shown how the resolution of an algorithm can be determined from its modulation transfer function (MTF), and how the MTF can be manipulated with the selection of intensity weighting windows. The random error levels for selected algorithms are demonstrated under different image and flow field conditions, including the near boundary region, using simulated PIV images.     

基于简易PIV的圆柱绕流压力场重构

采用简易粒子成像测速仪(PIV)装置测量入口流速为14.3 cm/s时圆柱绕流的速度场,运用有限容积法和直接积分法重构压力场。对比Fluent模拟速度场结果,分析简易PIV的速度场测量误差;对比Fluent模拟压力场结果,分析基于Fluent模拟速度场以及PIV实测速度场的不同算法重构压力场误差。结果表明:在简易PIV系统中,摄像机采用适合的空间分辨率与时间分辨率能有效减小速度场测量误差。基于Fluent模拟速度场数据,当给定第一边界条件时,有限容积法的压力场重构误差小于直接积分法,均方根误差分别为1.73%,8.99%;基于PIV实测速度场,有限容积法的压力场重构误差大于直接积分法,均方根误差分别为26.58%,12.72%;降低速度场误差与获取准确的边界条件均能有效提高压力场重构精度。通过采用低成本的PIV装置,探究获取流体的瞬态压力场重构方法,降低了PIV中重构压力场的成本。     

CRITERION OF STOCHASTIC LAYER NEAR A PLANAR HOMOCLINIC ORBIT OF NONLINEAR DYNAMICAL SYSTEM

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不同光照条件下作物蒸腾量计算的研究

作物蒸腾量的计算是水资源开发利用和农业生产运筹的关键参数之一。本文以彭曼-蒙特斯方程为基础，通过引入临界阻力，根据实测资料建立冠层阻力和空气动力学阻力比值与临界阻力和空气动力学阻力比值二者之间的函数关系，得到一个只需气象参数就能计算作物蒸腾量的简单方法。文章对该方法进行了理论分析，并用实例给予验证。结果表明，该方法在理论上和实践上都是可行的，是一个值得研究和发展的新方法。作物蒸腾量的日变化表明，炎热夏季晴天中午遮光处理后作物蒸腾量的增大是可能的。     

流域产流事件模型—论水文模型的简化

本文着重流域产流的主要环节，以流域下渗容量分配曲线与产流过程的关系为依据，吸收斯坦福流域水文模型的优点，简化总体结构，改进提高，减少模型参数，并与常规的前期影响雨量算法结合起来，建立流域产流事件模型。此模型只有４个优选参数，它克服了现有模型计算复杂和难于掌握应用等缺点，力求简便易行，能用于实际洪水预报，提高使用效果。在汉江支流丹江和洵河两个流域应用此模型，共模拟了２１年１０２次洪水，并用６年２６次洪水资料检验模型；又在汉江月河与渠江州河东林站应用此模型，它们的产流合格率均达８０％以上，经验表明，此模型简便易行，使用效果好，是值得研究推广的新模型。     

简易粒子图像测速(PIV)技术开发与优化技巧

粒子图像测速(PIV)技术是一种瞬态流动平面二维速度场测试技术,在细部流场实测领域得到重视,但是成熟的PIV产品价格高昂。鉴于此,介绍了一种简易的PIV装置,主要由高速摄像机、激光发射器、柱面透镜和示踪粒子构成,以较低成本即可基本实现商业用PIV产品的功能。为了验证简易PIV性能,设计了PIV简易装置,采用Fluent软件模拟,并结合PIV技术对比分析了简易PIV装置的优缺点,同时对影响结果的粒径大小和粒子跟随性进行了优化。结果表明,简易PIV装置适宜选用玉米粉作为示踪粒子,并需要根据示踪粒子跟随性所能达到的最大进口水流速度选择高速摄像机的帧率,最终能够较好地实现流场实测,进而达到对PIV技术进行开发和优化的目的,其分析结果将为后续研究者提供参考。     

PIV EXPERIMENTAL RESEARCH OF INSTANTANEOUS FLOW CHARACTERISTICS OF CIRCULAR ORIFICE SYNTHETIC JET

The instantaneous flow characteristics of circular orifice synthetic jet was experimentally studied by a phase-locked Particle Image Velocimetry (PIV) system. The instantaneous flowfields, including the forming, developing and breaking down of the vortex for the jet were clearly shown by the PIV experimental results. As the basis of the study of the instantaneous flow, 36 images were taken and phase-averaged for each condition. The PIV experiment was mainly focused on the time evolution of the vortex pairs formed in the push cycle, the saddle point existing in the suck cycle, the variation of the centerline velocity in the whole cycle and the cross-stream velocity profiles and their self-similarity. Finally, the orifice depth was changed from 1.5 mm to 2 mm and 3.5 mm in order to study the effect of different orifice depths on the flow structure, which shows that at all stream wise sections, the peak of the mass flux and momentum flux increases as the orifice depth increases. Furthermore, the nondimensional distance of the mass flux from the exit is the maximum, while the nondimensional distance of the centerline velocity peak from the exit is the minimum, and nondimensional distance of the momentum flux from the exit section is between them.     

STUDY OF VORTEX CHARACTERISTICS OF THE FLOW AROUND A HORIZONTAL CIRCULAR CYLINDER AT VARIOUS GAP-RATIOS IN THE CROSS-FLOW

1. INTRODUCTION The flow around a horizontal circular cylinder near a plane boundary (fixed wall) is of great significance in Hydrodynamics. For instance, sewagepipelines in water body of rivers in environmental engineering, conveying pipelines and optica…     

SOLUTION OF THE ENSO DELAYED OSCILLATOR WITH HOMOTOPY ANALYSIS METHOD

An ENSO delayed oscillator is considered.The El Nino atmospheric physics oscillation is an abnormal phenomenon involved in the tropical Pacific ocean-atmosphere interactions.The conceptual oscillator model should consider the variations of both the eastern and western Pacific anomaly patterns.Using the homotopy analysis method,the approximate expansions of the solution of corresponding problem are constructed.The method is based on a continuous variation from an initial trial to the exact solution.A Maclaurin series expansion provides a successive approximation of the solution through repeated application of a differential operator with the initial trial as the first term.This approach does not require the use of perturbation parameters and the solution series converges rapidly with the number of terms.Comparing the approximate analytical solution by homotopy analysis method with the exact solution,we can find that the homotopy analysis method is valid for solving the strong nonlinear ENSO delayed oscillator model.     

采用PIV研究离心泵转轮内部瞬态流场

数字式PIV技术可以在瞬间记录下整个测量断面内的信息，从而为解决水泵转轮内非定常流动的难题奠定了良好的基础，代表着水力机械内部复杂流动测试技术的方向。本文将二维数字式PIV系统成功地应用于清水离心泵实验台，对一改型后的离心泵转轮内的瞬态流场进行了成功测量，测量结果充分表明了离心泵转轮内部流场的瞬态结构和非定常性。     

ANALYTICAL RESEARCH ON THE WAVE DIFFRACTION OF ARC-SHAPED FLOATING BREAKWATERS

1. INTRODUCTIONBreakwaters are generally constructed for thedissipation and reflection of incident wave energyin order to decrease the wave height to protect thecoast against the erosion and to decrease the forceacting on the coastal structures . Compared…     

EFFECT OF STREAMLINE CURVATURE AND SOME OTHER CONDITIONS ON THE TURBULENT STRUCTURES IN THE OTHER REGION OF AN OBSTACLE

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A HEMODYNAMIC MODEL AND A MATHEMATICAL METHOD TO CALCULATE THE DYNAMICS INDEX FOR CEREBRAL CIRCULATION

The dynamics indexes,playing an important role in the cerebral circulation,will be changed significantly compared with their normal range in many cerebrovascular disease.The geometrical parameters of cerebrovascular may be detected by DSA or MRA scan,but the hemodynamic parameters,such as,blood flow,artery resistance and compliance must be calculated by building hemodynamics model. The cerebral circular system that has four entrances for blood flow(two carotid and two vertebral arteries)and three communicating arteries is much different from the systematic ststem which has only one entrance,ic.,the aortic.The purpose of this study is to set up a hemodynamics model with lumped parameters to describe the cerebral circulation.From this model,we get its governing equations and present a new method to calculate the hemodynamics indexes in clinical application.