Numerical simulation of hydrodynamic characteristics during the diversion closure in a horizontal tunnel

Based on water inrush accident of 1841 working face of Desheng Coal Mine in Wu'an, Hebei province, China, an evaluation model of hydrodynamic characteristics of the project is set up and simulated using Matlab. It is assumed that the pipe flow would transform into seepage flow when the aggregates are plugged into the water inrush channel and the seepage flow would disappear along with grouting process. The simulation results show that the flow velocity will increase with an increase in height of aggregates accumulation body during the aggregates filling process; the maximum seepage velocity occurs on the top of plugging zone; and the water flow decreases with increasing plugging height of water inrush channel. Finally, the field construction results show that the water inrush channel can be plugged effectively by the compacted body prepared with aggregate and cement slurry.

Experimental and Numerical Investigations of the Hydrodynamic Characteristics, Twine Deformation, and Flow Field Around the Netting Structure Composed of Two Types of Twine Materials for Midwater Trawls

Nettings are complex flexible structures used in various fisheries.Understanding the hydrodynamic characteristics,de-formation,and the flow field around nettings is important to design successful fishing gear.This study investigated the hydrodynamic characteristics and deformation of five nettings made of polyethylene and nylon materials in different attack angles through numeri-cal simulation and physical model experiment.The numerical model was based on the one-way coupling between computational fluid dynamics(CFD)and large deflection nonlinear structural models.Navier-Stokes equations were solved using the finite volume ap-proach,the flow was described using the k-ωshear stress turbulent model,and the large deflection structural dynamic equation was derived using a finite element approach to understand the netting deformation and nodal displacement.The porous media model was chosen to model the nettings in the CFD solver.Numerical data were compared with the experimental results of the physical model to validate the numerical models.Results showed that the numerical data were compatible with the experimental data with an average relative error of 2.34%,3.40%,6.50%,and 5.80%in the normal drag coefficients,parallel drag coefficients,inclined drag coefficients,and inclined lift coefficients,respectively.The hydrodynamic forces of the polyethylene and nylon nettings decreased by approxi-mately 52.56%and 66.66%,respectively,with decreasing net solidity.The drag and lift coefficients of the nylon netting were appro-ximately 17.15%and 6.72%lower than those of the polyethylene netting.A spatial development of turbulent flow occurred around the netting because of the netting wake.However,the flow velocity reduction downstream from the netting in the wake region in-creased with increasing attack angle and net solidity.In addition,the deformation,stress,and strain on each netting increased with in-creasing solidity ratio.

Hydrodynamic Characteristics of the Biplane-Type Otter Board with the Canvas Through Flume−Tank Experiment

Hydrodynamic characteristics of a biplane-type otter board,equipped with nylon canvas of 2 mm in thickness was investigated through flume-tank experiment in this study.A series of predesigned structures with different gap-chord ratios G/c(0.75,0.90,1.05),stagger anglesθ(30°,45°,60°),and proportions of flexible area relative to the whole wing areaƒr(0,55%,65%,75%),at an aspect ratio of 2.0 and a camber ratio of 15%,were experimentally carried out.The results showed the solution referring to the usage of flexible canvas replacing part of rigid structure for the biplane-type otter board was efficient for the trawling in the middle or shallow water area.The improvement of lift and stability for the biplane-type otter board was concluded,and drag of the structure was reduced by 1.9%atƒr=55%.In addition,the coefficient of variation of the lift and drag coefficient at different current velocities were 2.69%and 2.28%,respectively,which was smaller than those at relatively large proportion of the flexible area.Compared with the other tested structures,the frame-type flexible structure with the gap-chord ratio of 0.9 and a stagger angle of 45°and the proportion of the flexible area of 55%,performed best,and its drag was reduced by 5.72%and lift increased by 4.8%,compared with the rigid biplane-type otter board at the angles of attack from 18°to 28°.

Hydrodynamic characteristics and particle tracking of 90° lateral intakes at an inclined river slope

Lateral intakes are common in rivers.The pump effciency and sediment deposition are determined by the local hydrodynamic characteristics and mainstream division width.The hydraulic characteristics of lateral withdrawal from inclined river slopes at different intake elevations should be investigated.Meanwhile,the division width exhibits significant vertical non-uniformity at an inclined river slope,which should be clarified.Hence,a three-dimensional(3-D)hydrodynamic and particle-tracking model was developed with the Open Source Field Operation and Manipulation(Open FOAM),and the model was validated with physical model tests for 90°lateral withdrawal from an inclined side bank.The flow fields,withdrawal sources,and division widths were investigated with different intake bottom elevations,withdrawal discharges,and main channel velocities.This study showed that under inclined side bank conditions,water entered the intake at an oblique angle,causing significant 3-D spiral flows in the intake rather than two-dimensional closed recirculation.A lower withdrawal discharge,a lower bottom elevation of the intake,or a higher main channel velocity could further strengthen this phenomenon.The average division width and turbulent kinetic energy were smaller under inclined side bank conditions than under vertical bank conditions.With a low intake bottom elevation,a low withdrawal discharge,or a high main channel velocity,the sources of lateral withdrawal were in similar ranges near the local inclined bank in the vertical direction.Under inclined slope conditions,sediment deposition near the intake entrance could be reduced,compared to that under vertical slope conditions.The results provide hydrodynamic and sediment references for engineering designs for natural rivers with inclined terrains.

Global cavitation and hydrodynamic characteristics of a composite propeller in non-uniform wake

The composite propeller has attracted much interest due to its excellent mechanical properties such as high specific stiffness and high specific strength,hence there is an increasing interest in utilizing the composite materials to improve the hydrodynamic and structural performance of marine propellers.The objective of this paper is to study the cavitation performance of composite propellers based on the unsteady simulation method considering the cavitation-composite structure interaction.The typical cavitation patterns around the composite propeller are studied,which include blade sheet cavitation and tip vortex cavitation.The unsteady flow characteristics of tip vortex cavitation and structural dynamic response of composite propeller are studied,and the mechanism of composite propeller for the cavitation suppression and efficiency improvement is revealed.The results show that compared with rigid propellers,composite propellers have smaller cavity volume and higher propulsion efficiency under the same conditions.The unsteady cavitating flow characteristics under non-uniform wake are periodic,and the phase lag of hydrodynamic coefficients of composite propeller can be observed compared with that of the rigid propeller.The bending-torsional coupling deformation of the composite propeller makes the pressure pulsation of the flow field gentler,which reduces the influence of the cavitation load on the composite propeller.

Recent progress in hydrodynamic characteristics research and application of annular centrifugal extractors

The annular centrifugal extractor(ACE)integrates mixing and separation.It has been widely used in many industrial fields because of its low residence time,compact structure,and high mass transfer efficiency.Most of the literature has focused on flow instabilities,flow visualization,and computational fluid dynamics simulations.More recently,research on hydrodynamic behavior and structural optimization has received widespread attention.With the development of ACE technology,applications have been broadened into several new areas.Hence,this paper reviews research progress regarding ACE in terms of hydrodynamic characteristics and the structural improvements.The latest applications covering hydrometallurgy,nuclear fuel reprocessing,bio-extraction,catalytic reaction,and wastewater treatment are presented.We also evaluate future work in droplet breakup and coalescence mechanisms,structural improvements specific to different process requirements,scaling-up methods,and stability and reliability after scaling-up.

Slip in Couette flow with pressure gradient:Theoretical and experimental investigation of hydrodynamic characteristics considering slip effect

A new slip velocity model based on molecular potential theory and macro-force analysis,which is applied in Couette flow with pressure gradient,is built up.The model is validated by later being introduced in hydrodynamic system to predict film distribution,which shows a good agreement with experimental data obtained from multi-beam intensity-based tests with Fe and Cu ball materials under accurate controlled temperature,load and different wall velocities.Results show that the slip length for Fe case is ignorable so it seems like no slip,but for Cu case,the slip length is large to make 20%discrepancy with no slip simulation and also behaves shear-dependently.Moreover,during the experimental cases when both Fe and Cu ball velocities rise from-133 mm/s to 1330 mm/s,the slip velocity changes its direction with entrainment velocity and thus contributes to first enhance and then diminish the hydrodynamic film,but due to slip length on Cu case varying largely than that on Fe case,the film from Cu case and from Fe case has a clear cross-point between uh=80 mm/s and uh=220 m m/s(ub is the ball speed).The results above support strongly that Cu surface will lead to stronger slip than Fe case because of its smaller solid-liquid interaction,and obviously slip will influence hydrodynamic characteristics prominently.

Comparison of Hydrodynamic Performances Between Single Pontoon and Double Pontoon Floating Breakwaters Through the SPH Method

A numerical study adopting the 2Dδ-SPH model is performed to compare the hydrodynamic characteristics of a single pontoon floating breakwater and a double pontoon floating breakwater.Numerical simulations are performed using theδ-SPH model and experimental tests are conducted to validate the numerical model.The numerical results of both the free surface elevations and motions of the floating breakwater are in good agreement with the experimental results.Numerical results show that when the pontoon drafts are larger,the double pontoon floating breakwater performs better in wave attenuations compared with the single pontoon floating breakwater,and for all the drafts,the amplitudes of motions including sway,heave and roll of the double pontoon floating breakwater is always smaller.In addition,increasing the spacing between the two pontoons can further reduce the amplitudes of pontoon motions and improve the wave attenuation ability of the double pontoon floating breakwater.

超音速超空泡射弹的空泡流型和流体动力特性研究

A supercavitating projectile is launched underwater with supersonic speed,and then,the speed decreases to transonic and subsonic conditions orderly because of the drag coming from surrounding water.The flow regime and hydrodynamic characteristics are significantly influenced by the flying speed,the influence laws in supersonic,transonic,and subsonic regions are totally different.These issues aren’t well studied.A numerical model consisting of VOF model,moving frame method and state equation of liquid is established to calculate the compressible supercavitation flow field,and validated by comparing with a published result.The influences of water compressibility and Mach number on supercavity shape and hydrodynamic characteristics are quantitatively summarized.The results show that the flying speed of supercavitating projectiles exerts significant influences on the flow regime,supercavity shape and hydrodynamic characteristics for the transonic and supersonic conditions.With the decrease of flying speed,the drag coefficient decreases gradually,and the dimensions of the supercavity near supercavitating projectiles significantly increases in the high-speed conditions.An underwater bow shock is numerically observed before the disk cavitator in supersonic condition.However,no obvious changes are found for the incompressible water cases with different speeds.For supersonic conditions,the supercavity near supercavitating projectiles of compressible water is smaller than that of incompressible water,the drag coefficient is larger,and the relative difference significantly increases with the flying speed.For the case of Ma 1.214,the relative difference of supercavity diameter at the tail section 3.98%,and the difference of the drag coefficient is 23.90%.

Theoretical and Experimental Study of A Coaxial Double-Buoy Wave Energy Converter

The double-body heave wave energy converter(WEC)is one of the most conducive devices to absorb the wave energy from relative motion while the law of which is not well understood.This paper makes an in-depth study on this wave energy converter,by means of the combination of theoretical analysis and physical model experiment.The hydrodynamic characteristics and energy capture of the double-buoy under constant and linear Power Take-Off(PTO)damping are investigated.Influences of absolute mass and mass ratio are discussed in the theoretical model.Relative displacement amplitude and average power output are tested in the experiment to analyze the effect of the wave period and outer buoy’s mass,while the capture width ratio(CWR)is also calculated.Results show that the wave period and mass of the buoys have a significant effect on the converter.Different forms of PTO damping have no influence on the optimal wave period and mass ratio of this device.It is recommended to select the double-buoy converter with a mass ratio of 0.80 and to place it in an area with the frequent wave period close to the natural period of the outer buoy to achieve the optimal energy capture.

CFD Simulation and Experimental Study of a New Elastic Blade Wave Energy Converter

Small moving vehicles represent an important category of marine engineering tools and devices(equipment)typically used for ocean resource detection and maintenance of marine rights and interests.The lack of efficient power supply modes is one of the technical bottlenecks restricting the effective utilisation of this type of equipment.In this work,the performance characteristics of a new type of elastic-blade/wave-energy converter(EBWEC)and its core energy conversion component(named wave energy absorber)are comprehensively studied.In particular,computational fluid dynamics(CFD)simulations and experiments have been used to analyze the hydrodynamics and performance characteristics of the EBWEC.The pressure cloud diagrams relating to the surface of the elastic blade were obtained through two-way fluid-solid coupling simulations.The influence of blade thickness and relative speed on the performance characteristics of EBWEC was analyzed accordingly.A prototype of the EBWEC and its bucket test platform were also developed.The power characteristics of the EBWEC were analyzed and studied by using the blade thickness and motion cycle as control variables.The present research shows that the EBWEC can effectively overcome the performance disadvantages related to the transmission shaft torque load and power curve fluctuations of rigid blade wave energy converters(RBWEC).

Numerical and experimental study on the hydraulic characteristics of a vertical axial pump under various clearances of flare tube

In order to investigate the characteristics of a vertical axial flow pump under various clearances of flare tube, the bell-shaped inlet and box culvert outlet channels with flare tube are studied numerically and experimentally. Then, the cases of inlet and outlet channels with the least hydraulic loss are selected to form an integral pump system, for which both numerical simulation and experimental investigation are carried out. The numerical results agree well with the experimental data. It is shown that the clearances of the interfaces between different components of the pump system have a significant impact on the internal flow structure, turbulent entropy and hydraulic performance of the inlet and outlet channels. For the cases of normalized bottom clearance less than 0.5 and normalized top clearance larger than 0.4, the internal flow and hydraulic performance indexes of inlet and outlet channels are relatively poor. There also exists a critical clearance in either inlet or outlet channel at which the hydraulic loss reaches the maximum. The results serve as an important reference for the design as well as safe and efficient operation of the vertical axial flow pump system.

Effects of alfalfa coverage on runoff,erosion and hydraulic characteristics of overland flow on loess slope plots

An evaluation of the interactions between vegetation,overland and soil erosion can provide valuable insight for the conservation of soil and water.An experiment was conducted to study water infiltration,runoff generation process,rate of sediment erosion,and hydrodynamic characteristics of overland flow from a sloping hillside with different draw-off discharges from alfalfa and control plots with 20°slope.The effect of alfalfa on runoff and sediment transport reduction was quantitatively analyzed.Alfalfa was discussed for its ability to reduce the overland flow scouring force or change the runoff movement.Compared to the bare-soil plots,alfalfa plots generated a 1.77 times increase in infiltration rate.Furthermore,the down-slope water infiltration rate for the bare soil plots was higher than in the up-slope,while the opposite was found in the alfalfa plots.In addition,alfalfa had a significant effect on runoff and sediment yield.In comparison to the control,the runoff coefficient and sediment transportation rate decreased by 28.3%and 78.4%in the grass slope,respectively.The runoff generated from the alfalfa and bare-soil plots had similar trends with an initial increase and subsequent leveling to a steady-state rate.The transport of sediment reduced with time as a consequence of the depletion of loose surface materials.The maximum sediment concentration was recorded within the first few minutes of each event.The alfalfa plots had subcritical flow while the baresoil plots had supercritical flow,which indicate that the capability of the alfalfa slope for resisting soil erosion and sediment movement was greater than for bare soil plots.Moreover,the flow resistance coefficient and roughness coefficient for the alfalfa plots were both higher than for the bare-soil plots,which indicate that overland flow in alfalfa plots had retarded and was blocked,and the flow energy along the runoff path had gradually dissipated.Finally,the ability to erode and transport sediment had decreased.

Perspective on liquid metal enabled space science and technology

With the rapid development of deep space exploration and commercial flight, a series of tough scientific and technological challenges were raised, which urgently require ever advanced technologies to tackle with. Recently, liquid metals, as a kind of newly emerging functional material, are attracting various attention and many breakthroughs have been made on earth. Such a scientific trend also suggests promising approaches for solving those extreme challenges in space environment. To fulfill the increasing needs thus involved, this article is dedicated to systematically introducing liquid metal material and its related disciplines into space science and technology. Firstly, existing application of liquid metal cooling for space nuclear power was summarized. Then, some potential space practices were tentatively put forward, such as liquid metal thermal interface medium,liquid metal phase change material, liquid metal convection cooling, metal alloy thermal storage, liquid metal electromagnetic shielding and liquid metal electronic printing. Fundamental as well as practical issues that would differ with earth were interpreted. Finally, potential liquid metal space experiments were proposed to investigate the liquid metal hydrodynamic characteristic, wettability and phase change mechanism in space physical environment. Overall, liquid metal enabled space science and technology investigation will not only help efficiently solve the current and future space technological problems, but also aid to stimulate the advancement of liquid metal space material science.

Flow-field analysis of a continuous gas-solid separation fluidized bed equipped with a moving scraper

Continuous gas-solid separation fluidized beds are one of the most widely used practical operation units for the dry separation of coal in China,particularly in Northwest China,and they can effectively promote the efficient and clean utilization of raw coal.In a continuous gas-solid separation fluidized bed,the bed flow field is the concrete manifestation of the fluidization characteristics.However,the complexity of the flow field increases under the action of a moving scraper.In this study,a combination of computational fluid dynamics(CFD)simulations and experimental measurements was used to study the changes in the flow field of a fluidized bed.The results showed that when the scraper moved,the local flow field(mainly characterized by the movement of medium particles)near the scraper was affected not only by the common airflow or bubbles,but also by the lateral driving force of the scraper.When the scraper speed was v_(l)<6.0 cm/s,it reduced the frequency of the formation of large bubbles and alleviated the random fluctuation of the nearby particle collision stress signals,which improved the fluidization stability of the bed.Additionally,the movement of the scraper affected the global flow field.The flow field shifted to the right near the scraper,with the direction of the scraper movement,while the flow field exhibited a leftward trend on the surface of the bed,accompanied by some vortices,in the middle and lower parts of the bed.Additionally,the critical height of the area,directly affected by the scraper,increased from 52 to 54 mm with an increase in its operating speed from v_(l)=2.96 cm/s to v_(l)=4.44 cm/s,respectively.This provides a theoretical basis for further understanding the hydrodynamic characteristics of fluidized beds.