基于水力学力的定位格架防勾挂设计研究

定位格架是组成燃料组件的重要部件之一,与上、下管座共同构成了整个组件的外部轮廓。为减小燃料组件吊装过程中的勾挂风险,外条带上设置导向翼已成为定位格架结构设计上的重大改进。本文主要从燃料组件在堆芯的水力学环境出发,基于定位格架在堆芯运行过程中长期承受横向水力载荷可能造成外条带变形的考虑,采用计算流体动力学(CFD)方法,研究了定位格架外条带所承受的水力作用力,并为缓解外条带的受力情况进行了研究和方案设计。研究结果表明,在外条带上开孔能有效减小两侧压差,开孔的位置向下游方向移动效果更明显,同时开孔尺寸增大也能进一步减小两侧压差;更进一步地,将开孔位置移动到刚凸处,其平衡外条带两侧压力的作用更显著,外条带刚凸的开孔设计能更大程度地缓解外条带的水力作用。这些措施将对减小由于水力学力导致的外条带变形起到积极作用,从而在换料时有望降低燃料组件吊装过程中的勾挂风险。

A Comparative Study on Hydrodynamic Performance of Double Deflector Rectangular Cambered Otter Board

In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.

关于森林生态功能评价的探讨

森林生态功能是无形的，无法通过市场交换实现其价值，但是森林生态功能既有营林成本，又是营林收入，需要对其进行正确评价．该文就森林生态功能评价的意义、评价指标和评价方法做扼要论述，以朱亭小流域为例对森林涵养水源、保护土壤、纳碳释氧等生态功能进行评价，并对森林生态功能评价存在的问题提出几点看法。

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.

Characteristics of a magnetic fluid seal and its motion in an axial variable seal gap

With suitable assumptions a hydrodynamic model for the magnetic fluid motion in an axial variable gap seal was con- structed, and the solution to the equations of the model was deduced. The characteristics of a magnetic fluid seal and its motion, including the speed and pressure distribution, and the seal capacity of a magnetic fluid rotating seal were systematically described. The factors affecting seal capacity and ways to improve seal capacity based on the hydrodynamic model are discussed. The basic condition for dynamic seal availability is presented. The rotating speed and radius of the shafts should be decreased. The work can provide proof of a seal design or suggest ways to improve the seal capacity of magnetic fluid seals.

Computation of one—dimensional consolidation of double layered ground using differential quadrature method

The authors give the solution to the problem of one-dimensional conso l idation of double-layered ground with the use of the differential quadrature me t hod. Case studies showed that the computational results for pore-water pressure in soil layer agreed with those of analytical solution; and that in the computat ional results for the interface of soil layer also agreed with those of the anal ytical solution except for the small discrepancies during shortly after the star t of computation. The advantages of the solution presented in this paper are tha t compared with the analytical solution, it avoids the cumbersome work in solvin g the transcendental equation for eigenvalues, and in the case of the Laplace transform s olution, it can resolve the precision problem in the numerical solution of long time inverse Laplace transform. Because of the matrix form of the solution in th is paper, it is convenient for formulating computational program for engineering practice. The formulas for calculating double-layered ground consolidation may be easily extended to the case of multi-layered soils.

Modeling of state parameter and hardening function for granular materials

A modified plastic strain energy as hardening state parameter for dense sand was proposed, based on the results front a series of drained plane strain tests on saturated dense Japanese Toyoura sand with precise stress and strain measurements along many stress paths. In addition, a unique hardening function between the plastic strain energy and the instantaneous stress path was also presented, which was independent of stress history. The proposed state parameter and hardening function was directly verified by the simple numerical integration method. It is shown that the proposed hardening function is independent of stress history and stress path and is appropriate to be used as the hardening rule in constitutive modeling for dense sand, and it is also capable of simulating the effects on the de-formation characteristics of stress history and stress path for dense sand.

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.

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.

Study on Hydraulic System Efficiency of Heaving-Buoy Wave Energy Converter

The hydraulic system is the key component in the widely used wave energy converters(WEC).In this paper,we theoretically analyze and describe our investigation of the efficiency of the hydraulic system by simulation and model testing of the combined heaving-buoy WEC.We derive a new governing equation that includes nonlinear hydraulic resistance in the power take-off(PTO).We conducted a physical model experiment based on a 100-kW prototype and applied a hydraulic system with an energy accumulator.The model test results reveal an important parameter related to efficiency with respect to nonlinear hydraulic resistance.We also studied the relationship between the efficiency and the initial conditions.Finally,based on our numerical simulation results,we discuss the effect on efficiency of the gas content of the hydraulic fluid and ways to reduce its impact.

CFD prediction of local scour hole around bridge piers

In order to predict the local scour hole and its evaluation around a cylindrical bridge pier, the computational fluid dynamics （CFD） and theories of sediment movement and transport were employed to carry out numerical simulations. In the numerical method, the time-averaged Reynolds Navier-Stokes equations and the standard k-e model were first used to simulate the three-dimensional flow field around a bridge pier fixed on river bed. The transient shear stress on river bed was treated as a crucial hydrodynamic mechanism when handling sediment incipience and transport. Then, river-bed volumetric sediment transport was calculated, followed by the modification of the river bed altitude and configuration. Boundary adaptive mesh technique was employed to modify the grid system with changed river-bed boundary. The evolution of local scour around a cylindrical bridge pier was presented. The numerical results represent the flow pattern and mechanism during the pier scouring, with a good prediction of the maximum scour hole depth compared with test results.

Coal pillar mechanics of violent failure in U.S. Mines

This paper seeks to enhance the understanding that the horizontal stresses build up and release during coal pillar loading and unloading(post-failure) drawing upon three decades of observations, geomechanical monitoring and numerical modeling in bump-prone U.S. mines. The focus is on induced horizontal stress in mine pillars and surrounding strata as highly stressed pillars punch into the roof and floor, causing shear failure and buckling of strata; under stiff stratigraphic units of some western US mines, these events could be accompanied by violent failure of pillar cores. Pillar punching eventually results in tensile stresses at the base of the pillar, facilitating transition into the post-failure regime; this transition will be nonviolent if certain conditions are met, notably the presence of interbedded mudstones with low shear strength properties and proper mine designs for controlling seismicity and dynamic loads. The study clearly shows high confining stress build-up in coal pillars resulting in up to twice higher peak vertical stress and high strain energy accumulations in some western US mines in comparison with peak stresses predicted using common empirical pillar design methods. It is the unstable release of this strain energy that can cause significant damage resulting from pillar dilation and ground movements. These forces are much greater than the capacity of most common internal support systems, resulting in horizontal stressinduced roof falls locally, in mines under unremarkable far-field horizontal stress. Attention should be placed on pillar designs as increasing support density may prove to be ineffective. This mechanism is analyzed using field measurements and generic finite-difference stress analyses. The study confirms the higher load carrying capacity of confinement-controlled coal seams in comparison with structurally controlled coal seams. Such significant differences in confining stresses are not taken into account when estimating peak pillar strength using most common empirical techniques such as those proposed by Bieniawski and Salamon. While using lower pillar strength estimates may be considered conservative,it underestimates the actual capacity of pillars in accumulating much higher stress and strain energies,misleading the designer and inadvertently diminishing mine safety. The role of induced horizontal stress in mine pillars and surrounding strata is emphasized in coal pillar mechanics of violent failure. The triggering mechanism for the violent events is sudden loss of pillar confinement due to dynamic loading resulting from failure of overlying stiff and strong strata. Evidence of such mechanism is noted in the field by observed red-dust at the coal-rock interfaces at the location of coal bumps and irregular, periodic caving in room-and-pillar mines quantified through direct pressure measurements in the gob.

Using CFD Software to Calculate Hydrodynamic Coefficients

Applications of computational fluid dynamic(CFD) to the maritime industry continue to grow with the increasing development of computers.Numerical approaches have evolved to a level of accuracy which allows them to be applied for hydrodynamic computations in industry areas.Hydrodynamic tests,especially planar-motion-mechanism(PMM) tests are simulated by CFD software-FLUENT,and all of the corresponding hydrodynamic coefficients are obtained,which satisfy the need of establishing the simulation system to evaluate maneuverability of vehicles during the autonomous underwater vehicle scheme design stage.The established simulation system performed well in tests.

Numerical modeling of hydrodynamic changes due to coastal reclamation projects in Xiamen Bay,China

Xiamen Bay in South China has experienced extensive coastal exploitation since the 1950s,resulting in some severe environmental problems.Local authorities now have completed or are implementing many environmental restoration projects.Evaluating the cumulative impact of exploitation and restoration activities on the environment is a complicated multi-disciplinary problem.However,hydrodynamic changes in the bay caused by such coastal projects can be characterized directly and definitively through numerical modeling.This paper assesses the cumulative effect of coastal projects on the hydrodynamic setting using a high-resolution numerical modeling method that makes use of tidal current speeds and the tidal prism as two hydrodynamic indices.Changes in tidal velocity and the characteristics of the tidal prism show that hydrodynamic conditions have declined from 1938 to 2007 in the full-tide area.The tidal current speed and tidal prism have decreased by 40% in the western part of the bay and 20% in the eastern part of the bay.Because of the linear relationship between tidal prism and area,the degraded hydrodynamic conditions are anticipated to be restored to 1972 levels following the completion of current and proposed restoration projects,i.e.33% and 15% decrease in the hydrodynamic conditions of 1938 for the western and eastern parts of the bay,respectively.The results indicate that hydrodynamic conditions can be restored to some extent with the implementation of a sustainable coastal development plan,although a full reversal of conditions is not possible.To fully assess the environmental changes in a region,more indices,e.g.,water quality and ecosystem parameters,should be considered in future evaluations.

Experimental and CFD Studies on the Performance of Microfiltration Enhanced by a Turbulence Promoter

This paper reports experimental and computational fluid dynamics(CFD) studies on the performance of microfiltration enhanced by a helical screw insert.The experimental results show that the use of turbulence pro-moter can improve the permeate flux of membrane in the crossflow microfiltration of calcium carbonate suspension,and flux improvement efficiency is strongly influenced by operation conditions.The energy consumption analysis indicates that the enhanced membrane system is more energy saving at higher feed concentrations.To explore the intrinsic mechanism of flux enhancement by a helical screw insert,three-dimensional CFD simulation of fluid flow was implemented.It reveals that hydrodynamic characteristics of fluid flow inside the channel are entirely changed by the turbulence promoter.The rotational flow pattern increases the scouring effect on the tube wall,reducing the particle deposition on the membrane surface.The absence of stagnant regions and high wall shear stress are respon-sible for the enhanced filtration performance.No secondary flow is generated in the channel,owing to the streamline shape of helical screw insert,so that the enhanced performance is achieved at relatively low energy consumption.

Reliability Improvements to Centrifugal Pump Performance in Conjunction with Inducers, CFD Comparative Study

In this research, centrifugal pump unit was analysed to study the effects of using inducers on its performance. Hydraulic tests were done to obtain the optimum hydraulic performance before and after using inducer. Two types of inducers were used in this work （axial, helical）. For this purpose, a test rig was specially designed with a pump system to investigate the parameters under consideration. Plots （H-Q） curves, （B.P.-Q） curves and （q-Q） curves were used to show the effect of pump performance with and without inducers. The present study introduces a simulation of centrifugal pump performance in conjunction with inducers using CFD （Computational Fluid Dynamics）, to compare it with experimentally observed values. The model investigates the impact of using inducers on the head and flow of the pump. The results of the CFD model and experimental are correlated well. Furthermore, the results help the decision makers of the pumps for future developments in pump performance assuring safe and reliable running condition of the water pumps. Also it may be used for more applications of larger head and flow pumps.

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.

Rheological numerical simulation for thermo-hydro-mechanical coupling analysis for rock mass

Under the environment of seepage field, stress field and temperature field interaction and influence, the three fields will not only produce coupling effect, but also have deformation with time due to the rheological behavior of rock mass. In the paper, based on the fundamental theories of rock mass coupling theory and rheological mechanics, the rheological model for fully coupled thermo-hydro-mechanical analysis for rock mass was set up, and the corresponding constitutive relationship, the conservation equation of mass and the conservation equation of energy were given, and the finite element formulas were derived for coupling analysis of rock mass. During establishing governing equations, rock mass was assumed approximately as macro-equivalent continuum medium. The obtained rheological numerical model for fully coupled thermo-hydro-mechanical analysis can be used for analyzing and predicting the long-term stability of underground caverns and slope engineering under the condition of thermo-hydro-mechanical coupling with rheological deformation.

Characterization on the hydrodynamics of a covering-plate Rushton impeller

A modified Rushton impeller with two circular covering-plates mounted on the upper and lower sides of the blades was designed.There are gaps between the plates and the blades.The turbulent hydrodynamics was analyzed by the computational fluid dynamics(CFD) method.Firstly,the reliability of the numerical model and simulation method was verified by comparing with the experimental results from literature.Subsequently,the power consumption,flow pattern,mean velocity and mixing time of the covering-plate Rushton impeller(RT-C) were studied and compared with the standard Rushton impeller(RT) operated under the same conditions.Results show that the power consumption can be decreased about 18%.Compared with the almost unchanged flow field in the lower stirred tank,the mean velocity was increased at the upper half of the stirred tank.And in the impeller region,the mean axial and radial velocities were increased,the mean tangential velocity was decreased.In addition,the average mixing time of RT-C was shortened about 4.14% than the counterpart of RT.The conclusions obtained here indicated that RT-C has a more effective mixing performance and it can be used as an alternative of RT in the process industries.

Study on Unsteady Hydrodynamic Performance of Propeller in Waves

The speed of a ship sailing in waves always slows down due to the decrease in efficiency of the propeller. So it is necessary and essential to analyze the unsteady hydrodynamic performance of propeller in waves. This paper is based on the numerical simulation and experimental research of hydrodynamics performance when the propeller is under wave conditions. Open-water propeller performance in calm water is calculated by commercial codes and the results are compared to experimental values to evaluate the accuracy of the numerical simulation method. The first-order Volume of Fluid(VOF) wave method in STAR CCM+ is utilized to simulate the three-dimensional numerical wave. According to the above prerequisite, the numerical calculation of hydrodynamic performance of the propeller under wave conditions is conducted, and the results reveal that both thrust and torque of the propeller under wave conditions reveal intense unsteady behavior. With the periodic variation of waves, ventilation, and even an effluent phenomenon appears on the propeller. Calculation results indicate, when ventilation or effluent appears, the numerical calculation model can capture the dynamic characteristics of the propeller accurately, thus providing a significant theory foundation forfurther studying the hydrodynamic performance of a propeller in waves.