混凝土重力坝-水库系统非线性动力响应试验研究

本文旨在通过小尺度模型(1:150)的实验室方法,研究混凝土重力坝-水库系统的非线性响应。为了保持相似性,采用适当的水泥、砂、膨润土和水的配比确定模型坝的特征,大坝-水库模型能够传递水库水的水动力,且无水渗透。研究分别对空水和满水情况下的大坝-水库系统进行试验,以观察大坝的基本行为、裂缝形成、裂缝张开、裂缝平面滑动和裂缝稳定性模型,采用损伤塑性模型进行数值分析。研究忽略了刚性坝基础的影响,计算了大坝模型的特征频率和由拉伸损伤引起的裂缝扩展,并与试验值进行了比较。结果表明,所建立的大坝-水库系统实验模型是准确的。

刮刀夹网成形器内刮除所产生的水动力学压力

此研究意在定量测定刮除压力分布，并探讨其对某些生产上使用的几何形状的刮刀缝隙内的压力脉冲的影响，结果表明，刮除压力的作用具有 极高的局部性，完整的模型预测出刮除作用使从毛布－刮刀接触点处沿着刮刀表面某些小距离降流水层的压力达到临界值，作用在下毛布上的刮除压力的振幅小于临界压力，但是以使刮刀升流时缝隙内产生压位差，压力区域的大小只有几毫米，取决于刮刀边缘的曲率半径，而鼻形半径对于最大刮降压力没有明显的作用，随着鼻形曲率半径的增加刮除压力作用的距离增大，这样将明显增加缝隙内的峰值压力脉冲，刮除压力迫使一部分水从底毛布排出，流回到毛布之间的成形缝隙中，但这个量很少，大约为排出水的10％，在某些操作条件下，在刮刀前导端的上毛布附近可产生真空，此真空作用能将水从上毛布中抽出，流回到上，下毛布之间的成形狭缝中。

轮胎厂动力站动力水控制系统改造

介绍了轮胎厂动力站在动力水系统压力稳定控制上的优化改造方法。在原有设备基础上,增加了1个AI4/AO2×8BIT模拟量输入/输出模块、2个DI16×DC24 V数字量输入模块,调整PLC硬件组态、重新调试控制系统,实现了稳定自动控制,降低了劳动强度,节约了成本。

浅水、有限水深、深水中超临界航速船舶的水压场计算方法和应用

超临界船舶航行产生的波浪以及水动力压力所引起的船舶航行安全、海洋或海岸工程稳定性等问题已引起人们的广泛关注。由于不同水深下的压力变化特性不同,计算方法也存在差异。本研究发展并测试了涵盖解析方法、有限差分方法、边界元方法等计算方法的计算程序,并结合CFD方法开展了相关计算研究。同时,将这四种计算方法的结果与实验结果进行对比分析,展现了各种方法的优点、精度和局限性。基于计算程序和CFD方法,高精度获取浅水、有限水深以及更深水的超临界航速船舶水压场特性,系统全面地为船舶、海洋等领域工程师和研究人员在开展超临界船舶航行相关问题研究时提供技术参考。

波浪中浮式生产储油船(FPSO)的运动与荷载计算

应用线性化Weibull概率密度函数分析得到设计波参数和根据三维源汇分布方法建立浮体运动与波浪荷载计算方法,完成了一浮式生产储油船(FPSO)在波浪中的运动响应和船体表面水动力压力分布以及总体荷载的概率特性的计算.该计算结果可用于基于耐波性的FPSO船体型线优化,以及作为船体强度有限元分析和系泊系统设计的根据.

Numerical simulation of dynamic pore pressure in asphalt pavement

For studying the driving role of dynamic pressure in water-induced damage of asphalt pavement, based on the fast Lagrangian finite difference method and Biot dynamic consolidation theory, fluid-solid coupling analysis of the pavement is conducted considering asphalt mixtures as porous media. Results reveal that the development and dissipation of the dynamic pore pressure are coinstantaneous and this makes both the positive and negative dynamic pore pressure and seepage force alternate with time. Repetitive hydrodynamic pumping and sucking during moisture damage is proved. The dynamic pore pressure increases with vehicle velocity. Effective stress and deflection of pavement decrease due to the dynamic pore water pressure. However, the emulsification and replacement of the asphalt membrane by water are accelerated. The maximum dynamic pore pressure occurs at the bottom of the surface course. So it is suggested that a drain course should be set up to change the draining condition from single-sided drain to a two-sided drain, and thus moisture damage can be effectively limited.

Investigation of Coolant Fluid through Grinding Zone in High-Speed Precision Grinding

In the grinding process,grinding fluid is delivered for the purposes of chip flushing,cooling,lubrication,and chemical protection of the work surface.Due to the high-speed rotation of the grinding wheel,a boundary layer of air forms around the grinding wheel and moves most of the grinding fluid away from the grinding zone.Hence,the conventional method of delivering coolant fluid that floods delivery with high fluid pressure and nozzle fluid rare supply coolant fluid to achieve high performance grinding.The flood grinding typically delivering large volumes of grinding fluid is ineffective,especially under high speed grinding conditions.In the paper,a theoretical model is presented for flow of grinding fluid through the grinding zone in high-speed precision grinding.The model shows that the flow rate through the grinding zone between the wheel and the workpiece surface not only depends on wheel porosity and wheel speed,but also depends on nozzle volumetric flow rate and fluid jet velocity.Furthermore,the model is tested by a surface grinding machine in order to correlate between experiment and theory.Consequently,the useful flow-rate model is found to give a good agreement with the experimental results and the model can well forecast the useful flow-rate in high-speed precision grinding.

Dynamic simulation and optimal control strategy for a parallel hybrid hydraulic excavator

The primary focus of this study is to investigate the control strategies of a hybrid system used in hydraulic excavators. First, the structure and evaluation target of hybrid hydraulic excavators are analyzed. Then the dynamic system model including batteries, motor and engine is built as the simulation environment to obtain control results. A so-called multi-work-point dynamic control strategy, which has both closed-loop speed PI (proportion integral) control and direct torque control, is proposed and studied in the simulation model. Simulation results indicate that the hybrid system with this strategy can meet the power demand and achieve better system stability and higher fuel efficiency.

Pulsating hydraulic fracturing technology in low permeability coal seams

Based on the difficult situation of gas drainage in a single coal bed of high gas content and low perme- ability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger movement and the mechanism of pulsating pressure formation using theoretical research, mathematical modeling and field testing. We analyze the effect of pulsating pressure on the formation and growth of fractures in coal by using the pulsating hydraulic theory in hydraulics. The research results show that the amplitude of fluctuating pressure tends to increase in the case where the exit is blocked, caused by pulsating pressure reflection and frictional resistance superposition, and it contributes to the growth of fractures in coal. The crack initiation pressure of pulsating hydraulic fracturing is 8 MPa, which is half than that of normal hydraulic fracturing; the pulsating hydraulic fracturing influence radius reaches 8 m. The total amount of gas extraction is increased by 3.6 times, and reaches 50 LJmin at the highest point. The extraction flow increases greatly, and is 4 times larger than that of drilling without fracturing and 1.2 times larger than that of normal hydraulic fracturing. The technology provides a technical measure for gas drainage of high gas content and low permeability in the single coal bed.

Measuring the Internal Velocity of Debris Flows Using Impact Pressure Detecting in the Flume Experiment

Measuring the internal velocity of debris flows is very important for debris flow dynamics research and designing debris flow control works. However, there is no appropriate method for measuring the internal velocity because of the destructive power of debris flow process. In this paper, we address this problem by using the relationship between velocity and kinetic pressure, as described by surface velocity and surface kinetic pressure data. Kinetic pressure is the difference of impact pressure and static pressure. The former is detected by force sensors installed in the flow direction at the sampling section. Observations show that static pressure can be computed using the formula for static water pressure by simply substituting water density for debris flow density. We describe the relationship between surface velocity and surface kinetic pressure using data from seven laboratory flume experiments. It is consistent with the relationship for single phase flow, which is the measurement principle of the Pitot tube.

Analysis and numerical simulation of dynamic effect on rock under high pressure water jet

Based on continuum mechanics and rock dynamics,analyzed the micro-struc- ture damage of rock and the impulsive effect under high pressure water jet and developed the dynamic model.Further,on the assumption of that rock was homogeneous and iso- tropic,a computational model was established based on nonlinear finite element and Arbi- trary Lagrangian-Eulerian(ALE) method.The dynamic effect impacted on rock under high pressure water jet was simulated by the dynamic contact method.The propagation of stress wave in rock was numerically simulated at different impacting velocity.The results show that the propagation velocity of stress wave is proportional to the impacting velocity of high pressure water jet.The faster the impacting velocity is,the quicker the comedown of stress wave.

On the method of the automatic modeling in hydraulic pipe networks

In this paper the dynamic characteristics in pipes are analyzed with frequency method, and puts forward a simple and practical describing method. By establishing the model library beforehand, the modeling of the pipe net is completed automatically, and we can accurately calculate the impedance characteristics of the pipe network, achieve the reasonable configuration of the pipe network, so that to decrease the pressure pulsation.

Pore pressure fluctuations of overlying aquifer during residual coal mining and water-soil stress coupling analysis

Three test models and a simulation model were constructed based on the prevailing conditions of the Taiping coalmine in order to analyze pore pressure fluctuations of an overlying aquifer during residual coal mining. As well, the relation between pore pressure and soil stress was evaluated. The model tests show the vibrations of pore pressure and soil stress as a result of mining activities. The simulation model tells of the response characteristics of pore pressure after mining and its distribution in the sand aquifer. The comparative analysis reveals that pore pressure and soil stress vibration are activated by unexpected events occurring in mines, such as collapsing roofs. An increased pore pressure zone always lies above the wall in front or behind the working face of a mine. Both pore pressure and vertical stress result in increasing and decreasing processes during movements of the working face of a mine. The vibration of pore pressure always precedes soil stress in the same area and ends with a sharp decline. Changes in pore pressure of sand aquifer are limited to the area of stress changes. Obvious changes are largely located in a very small frame over the mining face.

Analytical solution for slope instability assessment considering impact of confined aquifer

An analytical approach was presented for estimating the factor of safety(FS) for slope failure, with consideration of the impact of a confined aquifer. An upward-moving wetting front from the confined water was assumed and the pore water pressure distribution was then estimated and used to obtain the analytical expression of FS. Then, the validation of the theoretical analysis was applied based on an actual case in Hong Kong. It is shown that the presence of a confined aquifer leads to a lower FS value, and the impact rate of hydrostatic pressure on FS increases as the confined water pressure increases, approaching to a maximum value determined by the ratio of water density to saturated soil density. It is also presented that the contribution of hydrostatic pressure and hydrodynamic pressure to the slope stability vary with the confined aquifer pressure.

The urban unsteady and non-pressure rain pipe flow routing by the dynamical-wave method

The dynamical-wave routing model of the urban unsteady and non-pressure rain pipe flow was established by conservation of mass, momentum and energy, and it was solved by applying the four point implicit difference method and the pursuit method. It was obtained from the experiment checking and comparative analysis that the dynamical-wave muting model can reflect influence like attenuate and backwater when flood peak propagate in pipeline with high calculation precision and vast application scope, and it can be applied in routing of urban rain pipe flow of different slopes and inflow conditions. The routing model supplies a scientific foundation for the town rainfall piping design or checking, disaster administration of storm runoff, and so on.

Hydrodynamics numerical investigation of hoistable masts for underwater vehicles

Using the unsteady incompressible Navier-Stokes equation as the governing equation, the large eddy simulation (LES) model is implemented to investigate the shedding of vortices, the flow pattern of turbulence, the unsteady pressure fluctuation and the time history of the lift coefficient and drag coefficient of hoistable masts with various mast shapes and various arrangements in this paper. Combining the FFT, combined time-frequency transform and wavelet power spectrum analysis, the characteristics of unsteady pressure can be obtained in both time and frequency domain. It shows that the main frequency of pressure fluctuation is near the frequency of vortex shedding in time domain using the FFT method. It can be inferred from the combined time-frequency transform that the unsteady pressure fluctuation has obviously the peak value and the second peak value in time domain. It could indicate that the fluctuation power varies from the fluctuation frequency through the power spectrum analysis. By the data analysis, it shows that the vortex shedding is the dominant cause of the periodically pressure fluctuation. And the interaction pattern of wake and interplay between wake and the walls of masts under different arrangements are also discussed in this paper.

Pressure fluctuation propagation of a pump turbine at pump mode under low head condition

Pressure fluctuation at the vaneless space and vanes passages is one of the most important problems for the stable operation of a pump turbine. The fluctuation appears in any operating condition. Much research has been done on the pressure fluctuation of hydraulic machinery. However, the details of pressure fluctuation propagation of the pump turbine at the pump mode have not been revealed. The modem pump turbine with high water head requires the runner to be ＂flat＂, which would induce pressure fluctuation more easily than the low head pump turbine. In this article, a high head pump turbine model is used as the re- search object. As the pressure fluctuation at off-design point is more serious than at the design point, the low head condition is chosen as the research condition. Pressure fluctuation at the vaneless space and vanes passages is predicted by the computa- tional fluid dynamics method based on k-co shear stress transport model. The experiment conducted on the test rig of the Har- bin Institute of Large Electrical Machinery is used to verify the simulation method. It proves that the numerical method is a feasible way to research the fluctuation under this operating condition. The pressure fluctuation along the passage direction is analyzed at time and frequency domains. It is affected mainly by the interaction between the runner and vanes. In the circumferential direction, the influence of the special stay vane on the pressure fluctuation is got. The amplitude in the high-pressure side passage of that vane is lower than that in the other side. The study provides a basic understanding of the pressure fluctua- tion of a pump turbine and could be used as a reference to improve the operation stability of it.

A new depth-integrated non-hydrostatic model for free surface flows

A new depth-integrated model deploying a non-hydrostatic pressure distribution is presented.With the pressure divided into hydrostatic and dynamic components,the horizontal momentum equations were obtained by integrating the Navier-Stokes equations from the bottom to the free surface.The vertical momentum equation,in which the convective and viscosity terms were omitted,was approximated by the Keller-box scheme.The model has two steps.First,the dynamic pressure gradient terms were discretized semi-implicitly and the other terms were in explicit scheme.Second,the velocities expressed as the unknown dynamic pressure were substituted into the continuity equation,resulting in a five-diagonal symmetric matrix linear system that was solved by the conjugate gradient method.The model was validated with the propagation of a solitary wave and sinusoidal wave,indicating that it can predict free surface flows well.

Influence of Separated Vortex on Aerodynamic Noise of an Airfoil Blade

In order to clarify the mechanism by which aerodynamic noise is generated from separated flow around an airfoil blade,the relation between the attack angle and the aerodynamic noise of the blade was analyzed using a wind tunnel experiment and a CFD code.In the case of rear surface separation,the separated vortex which has a large-scale structure in the direction of the blade chord is transformed into a structure that concentrates at the trailing edge with an increase in the attack angle.The aerodynamic noise level then becomes small according to the vortex scale in the blade chord.When the flow is separated at the leading edge,a separated vortex of low pressure is formed at the vicinity of the trailing edge.The pressure fluctuations on the blade surface at the vicinity of the trailing edge become large due to the vortex in the wake.It is considered that the aerodynamic noise level increases when the flow is separated at the leading edge because the separated vortex is causing the fluctuations due to wake vortex shedding.

Jeans Instability of Self Gravitating Dust Cloud in Presence of Effective Electrostatic Pressure

The role of viscosity coefficient(η′), coulomb coupling parameter(Γ) and dust mass on the growth of jeans mode is investigated in strongly coupled dusty plasma using equations of Generalized Hydrodynamics(GH) Model. The novel aspect of this work is that the force arising due to electrostatic pressure caused by grain grain interaction has been included in the dynamics of dust particles. This force is found to play a significant role in counter balancing the self gravity effect, thereby reducing the growth rate of jeans instability. The present work may provide more physical insight in understanding the mechanisms behind formation of planetesimals, stars etc.