EXPERIMENTAL ESTIMATION OF A SCALING EXPONENT FOR TIP VORTEX CAVITATION VIA ITS INCEPTION TEST IN FULL- ANDMODEL-SHIP

Tip vortex cavitation noise of marine propeller became primary concerns to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model-and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full-and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy.     

河北太行山区泥石流启动的水岩相互作用

泥石流作为一种固-液混合而形成的地质灾害,其启动过程中必然存在着水与岩土体之间的相互作用。根据对太行山区泥石流形成的地形地貌、降雨、物源和人类活动特征等影响因素的分析,确定太行山区泥石流的崩滑动力和洪水动力两种启动类型。在此基础上,从水-岩系统耦合作用的角度,研究了太行山区泥石流形成过程中,洪水与固体颗粒之间彼此促进、相互制约的水岩化学作用、水岩物理作用和水岩力学作用,阐明了水岩相互作用对泥石流初始形成的促进机制,从而为泥石流启动预测预报体系的建立提供理论支撑。     

调距桨梢涡精细流场的数值模拟

为验证湍流粘度取为mk/的修正剪切应力输运(SST)湍流模型在螺旋桨梢涡精细流场粘性模拟中的适用性,对驱逐舰母型桨DTMB5168调距桨的梢涡流动进行了模拟与校验。结果显示:0.9R以上径向区域周向平均的轴向、周向和径向速度分量均与试验值吻合很好,但0.9R以下区域的径向速度分量存在一定偏差;0.7R和0.92R处沿周向变化的三个速度分量变化形态均与试验值一致,故可由此来确定梢涡涡核区,但周向和径向速度分量峰值比试验值略小;轴向0.3R距离内梢涡涡核运动轨迹的模拟结果与试验值吻合较好。由此证明了修正的SST湍流模型在螺旋桨梢涡流动模拟中的适用性,还表明由叶梢区的径向、周向和轴向方向以及桨叶近壁面法向、叶截面弦长方向和尾流轴向方向的网格节点密度来局部控制叶梢区流动的模拟效果的可行性。     

大庆长垣中部扶杨油层断裂对储层的控制作用

通过对大庆长垣中部杏树岗、高台子和太平屯构造扶杨油层的断裂和砂体展布特征分析认为,扶杨油层的断裂与砂体具有相互作用关系,即同沉积断裂对砂体的展布具有控制作用,而河道沉积的砂体对断裂形成具有制约作用。断裂与砂体的相互作用对扶杨油层油气运移和成藏具有重要意义,同沉积断裂控制的砂体以垂向向下排烃为主,形成低部位成藏模式,河道砂体与其诱导的断裂共同构成了垂向向上和侧向运移的通道,形成高部位成藏模式。     

Hydrodynamics of the Low-Energy Separator

Abstract

The hydrodynamics and operational principle of the low-energy separator are described. This separator has two stages of separation: pre-separation and a twin separation unit composed of vortex-type separators. Multi-phase flow is fed to a pre-separation pipe designed to create stratified flow. Next, the stratified flow is split up into two streams, one formed mainly by gas and liquid, and another formed mainly by liquid and solid. These streams are diverted toward a twin vortex-type separator where each stream is separated into its individual phases. A three-layer model is used to study the pre-separation process, and a mechanistic-lagrangian model is used to analyze the flow into the twin-separation unit. The device is intended for use on facilities where the space is limited. Potential application of this separator includes, but is not restricted to, separation of multi-phase flows in surface equipment of under-balanced drilling, and in oil production facilities.     

The Thermodynamic Modeling of Asphaltene Precipitation Equilibrium during the Natural Production of Crude Oil: The Role of Pressure and Temperature

Asphaltene precipitation is a sophisticated issue in the upstream oil industry, worldwide, and has detrimental effect on a verity of production processes; it damages the properties of the reservoir and causes an unfavorable and significant decrease in oil production. In spite of numerous studies to predict asphaltene behavior, the effect of temperature on asphaltene precipitation during pressure depletion at reservoir conditions is still obscure in the literature. In this study the PVT data as well as experimental data of asphaltene precipitation at reservoir conditions of an Iranian light oil samples is used, and the asphaltene precipitation and deposition envelops (APE and ADE) of the oil are developed using solid thermodynamic modeling.     

An Experimental Investigation of Fracture Tilt Angle Effects on Frequency and Stability of Liquid Bridges in Fractured Porous Media

Abstract

Liquid bridges are believed to play an important role in improving the recovery of fractured reservoirs. However, little is known about the stability of liquid bridges in fractured media at the pore scale. In this work, a glass micromodel representing a stack of two blocks was used at different tilt angles to monitor the frequency and stability of liquid bridges formed during free-fall gravity drainage as a function of tilt angle. It was observed that by increasing the tilt angle, the liquid bridge frequency decreased but its stability increased. This resulted in higher ultimate recovery. In addition, it was found that during the first half of the experiments, the number of bridges was higher but their stability was lower than during the second half of the tests. Moreover, no more than one stable liquid bridge was observed at tilt angles above 20°, and the bridge cross-sectional area was gradually decreased as the stability was maintained. A sequence of bridges that were formed and broken one after the other results in a higher drainage rate than a single bridge with stability equal to the overall stability of the sequence.     

Characteristics of heat dissipation from photovoltaic cells on the bottom wall of a horizontal cabinet to ambient natural convective air stream

This study proposes a model to investigate the behaviors of natural convective cooling of photovoltaic cells mounted discretely on the bottom wall of a horizontal cabinet. The effects of Rayleigh number (Ra), dimensionless length of cabinet (C_x), ratio of cabinet wall to air thermal conductivities (K_ef), number of photovoltaic cells (N), emissivity of metal wall (ε_e), and emissivity of glass lens (ε_g) are explored. Furthermore, the importance of thermal interaction between air streams inside and outside the cabinet through conducting wall are examined. The numerical computation domain covers the cabinet and surrounding area, so that the temperature and velocity fields of the combined regions are solved simultaneously. Results show that temperature differences among the photovoltaic cells can be up to 28% for all the investigated cases when 10⁶ ≦ Ra ≦ 10⁸, 5 ≦ C_x ≦ 12.5, 4 ≦ N ≦ 10, 1000 ≦ K_ef ≦ 6300, 0 ≦ ε_e ≦ 0.5 and 0 ≦ ε_g ≦ 0.94. The maximum difference in hot spot temperatures of photovoltaic cells is about 26% among the cases with various K_ef. In addition, the temperatures are rather low for the situation without consideration of thermal interaction between the air streams inside and outside the cabinet. Therefore, without the consideration of the thermal interaction would cause serious under-prediction for the hot spot temperatures of photovoltaic cells in engineering applications.     

青海电网HVDC辅助频率控制研究

基于电力系统分析软件包PSASP,使用其用户自定义功能,建立了辅助频率控制模型。该模型为青藏直流联网工程用户自定义高压直流输电模型的一部分。通过在2011年青海与西藏联网数据中应用,仿真验证了辅助频率控制用户自定义模型对于改善整流侧及逆变侧交流系统的频率、提高交直流系统的安全稳定性的正确性及必要性。     

基于MapX的电力系统GIS人机交互设计

应用基于地理信息系统(GIS)的电力系统可视化界面开发方法,使用MapInfo软件,设计绘制包括基础地理层、发电厂层、变电站层、220 kV输电线路层、500 kV输电线路层的GIS图.在此基础上,实现基于MapX的电力系统GIS人机交互基本功能及高级功能,基本功能包括空间功能、查询功能、详细数据展示功能、专题图功能、鹰眼图功能、等高线图功能、3D可视化功能,高级功能包括关联多屏显示功能、自适应调节功能.在整个系统中,基本功能可以较为简单地进行实现;高级功能突破了简单的二次开发限制,针对性更强,且具备了更专业的人机交互功能.依据电力系统中不同的使用特点和需求,还可以在此基础上开发出更多的其他高级功能.在对电网数据进行管理、分析和维护时具有显著的效果.