Showing papers in "Journal of Hydrodynamics in 2014"
TL;DR: In this paper, the authors summarized the physical background of such limitations and their combination in terms of the Morton number is presented and discussed, resulting in a series of more conservative recommendations for air concentration scaling.
Abstract: Physical modeling represents probably the oldest design tool in hydraulic engineering together with analytical approaches. In free surface flows, the similitude based upon a Froude similarity allows for a correct representation of the dominant forces, namely gravity and inertia. As a result fluid flow properties such as the capillary forces and the viscous forces might be incorrectly reproduced, affecting the air entrainment and transport capacity of a high-speed model flow. Small physical models operating under a Froude similitude systematically underestimate the air entrainment rate and air-water interfacial properties. To limit scale effects, minimal values of Reynolds or Weber number have to be respected. The present article summarizes the physical background of such limitations and their combination in terms of the Morton number. Based upon a literature review, the existing limits are presented and discussed, resulting in a series of more conservative recommendations in terms of air concentration scaling. For other air-water flow parameters, the selection of the criteria to assess scale effects is critical because some parameters (e.g., bubble sizes, turbulent scales) can be affected by scale effects, even in relatively large laboratory models.
99 citations
TL;DR: Results show that both the MPS and level-set methods are good tools for simulation of violent sloshing flows, however, the second pressure peaks as well as breaking and splashing of free surface by the M PS method are captured better than by the level- set method.
Abstract: This paper presents a comparative study of a meshless moving particle semi-implicit (MPS) method and a grid based level-set method in the simulation of sloshing flows. The numerical schemes of the MPS and level-set methods are outlined and two violent sloshing cases are considered. The computed results are compared with the corresponding experimental data for validation. The impact pressure and the deformations of free surface induced by sloshing are comparatively analyzed, and are in good agreement with experimental ones. Results show that both the MPS and level-set methods are good tools for simulation of violent sloshing flows. However, the second pressure peaks as well as breaking and splashing of free surface by the MPS method are captured better than by the level-set method.
80 citations
TL;DR: In this paper, a filter-based density correction model (FBDCM) was proposed to reduce the turbulent eddy viscosities in a turbulent cavitating flow based on the local meshing resolution and the local fluid density.
Abstract: In this paper, various turbulence closure models for unsteady cavitating flows are investigated. The filter-based model (FBM) and the density correction model (DCM) were proposed to reduce the turbulent eddy viscosities in a turbulent cavitating flow based on the local meshing resolution and the local fluid density, respectively. The effects of the resolution control parameters in the FBM and DCM models are discussed. It is shown that the eddy viscosity near the cavity closure region can significantly influence the cavity shapes and the unsteady shedding pattern of the cavitating flows. To improve the predictions, a Filter-Based Density Correction model (FBDCM) is proposed, which blends the FBM and DCM models according to the local fluid density. The new FBDCM model can effectively represent the eddy viscosity, according to the multi-phase characteristics of the unsteady cavitating flows. The experimental validations regarding the force analysis and the unsteady cavity visualization show that good agreements with experimental visualizations and measurements are obtained by the FBDCM model. For the FBDCM model, the attached cavity length and the resulting hydrodynamic characteristics are subsequently affected by the detail turbulence modeling parameters, and the model is shown to be effective in improving the overall predictive capability.
67 citations
TL;DR: In this article, the authors investigated the pressure loading to a high head (Hp = 377 m, Dp = 1.78 m) Francis turbine during start-stop and found that the maximum pressure amplitudes are about 14 kPa and 16 kPa from the instantaneous mean value of 121 kPa during rapid start-up and shutdown, respectively.
Abstract: Penetration of the power generated using wind and solar energy to electrical grid network causing several incidents of the grid tripping, power outage, and frequency drooping. This has increased restart (star-stop) cycles of the hydroelectric turbines significantly since grid connected hydroelectric turbines are widely used to manage critical conditions of the grid. Each cycle induces significant stresses due to unsteady pressure loading on the runner blades. The presented work investigates the pressure loading to a high head (Hp = 377 m, Dp = 1.78 m) Francis turbine during start-stop. The measurements were carried out on a scaled model turbine (HM = 12.5 m, DM = 0.349 m). Total four operating points were considered. At each operating point, three schemes of guide vanes opening and three schemes of guide vanes closing were investigated. The results show that total head variation is up to 9% during start-stop of the turbine. On the runner blade, the maximum pressure amplitudes are about 14 kPa and 16 kPa from the instantaneous mean value of 121 kPa during rapid start-up and shutdown, respectively, which are about 1.5 times larger than that of the slow start-up and shutdown. Moreover, the maximum pressure fluctuations are given at the blade trailing edge.
64 citations
TL;DR: The analysis suggests that there are just a little differences in the turbine outer characteristics, thus the traditional 1-D method is in general acceptable, however, the flow patterns in the spiral casing, the draft tube, and the runner passages are quite different: the transient situation has obvious water hammer waves, the water inertia, and some other effects.
Abstract: This paper presents the simulation and the analysis of the transient process of a Francis turbine during the load rejection by employing a one-dimensional and three-dimensional (1-D-3-D) coupling approach. The coupling is realized by partly overlapping the 1-D and 3-D parts, the water hammer wave is modeled by defining the pressure dependent density, and the guide vane closure is treated by a dynamic mesh method. To verify the results of the coupling approach, the transient parameters for both typical models and a real power station are compared with the data obtained by the 1-D approach, and good agreements are found. To investigate the differences between the transient and steady states at the corresponding operating parameters, the flow characteristics inside a turbine of the real power station are simulated by both transient and steady methods, and the results are analyzed in details. Our analysis suggests that there are just a little differences in the turbine outer characteristics, thus the traditional 1-D method is in general acceptable. However, the flow patterns in the spiral casing, the draft tube, and the runner passages are quite different: the transient situation has obvious water hammer waves, the water inertia, and some other effects. These may be crucial for the draft tube pulsation and need further studies.
53 citations
TL;DR: In this paper, the authors developed a new methodology to predict the stage discharge relationship specifically for wide compound channels using Darcy's friction factor (f) for the main channel and flood plain regions.
Abstract: Results of research into a compound channel having width ratio (α) in excess of 11 are presented in the form of boundary shear distributions across the compound cross section. New relationship is derived between the percentage of shear carried by the flood plains (%S
fp) and the percentage of area occupied by the flood plains (%A
fp). The equation so derived is taken as the basis to develop a new methodology to predict the stage discharge relationship specifically for wide compound channels using Darcy’s friction factor (f) for the main channel and flood plain regions. The methodology also is used for compound channels with smaller width ratios by applying the appropriate relation for %S
fp derived earlier by different researchers and seems to work well. Next, as a corollary to the methodology, separate formulae are proposed to estimate flow distribution in main channel and flood plain regions. The proposed method and its corollary are tested for their validity against well-published small-scale data series of previous researchers along with some large-scale data series from EPSRC-FCF (A-Series) compound channel experiments and very good agreement is observed between the measured values and predicted values for total flow as well as zonal distribution of flow. The methodology is also applied to some compound river section data published in literature and is found to serve well the purpose of predicting flow in real world application. This new method gives the least RMS value of error for discharge prediction compared with some other well-known methods used for estimating stage-discharge relation in compound channels by considering all data sets.
48 citations
TL;DR: In this article, the removal of contaminants including nutrients, metals and organic pollutants by vegetations in aquatic environments is discussed and the removal efficiencies with respect to 16, 19 and 14 kinds of different aquatic plants, respectively in three tables.
Abstract: This paper reviews the removal of contaminants including nutrients, metals and organic pollutants by vegetations in aquatic environments. The removal efficiencies are considered with respect to 16, 19 and 14 kinds of different aquatic plants, respectively in three tables. Due to different characteristics, the removal effects of plants on contaminants from the overlying water differ greatly. The vegetation can improve the water quality mainly through two ways: (1) to adsorb and absorb pollutants from water, (2) to prevent pollutants from releasing from sediment. The contaminant removal mechanisms of vegetations and related physical, chemical and biological effects are discussed. The effects of vegetations on the contaminant removal are found to depend on the environmental conditions, the number and the type of plants, the nature and the chemical structure of the pollutants. In addition, the contaminant release and removal by vegetations under hydrodynamic conditions is specially addressed. Further research directions are suggested.
42 citations
TL;DR: In this article, the hydrodynamic characteristics of a spar-type wind turbine known as the OC3-Hywind concept and the dynamic responses of the turbine were investigated under different sea states and the effects of the loads induced by the wind and the wave on the system were discussed.
Abstract: Due to the energy crisis and the environmental issues like pollution and global warming, the exploration for renewable and clean energies becomes crucial. The offshore floating wind turbines (OFWTs) draw a great deal of attention recently as a means to exploit the steadier and stronger wind resources available in deep water seas. This paper studies the hydrodynamic characteristics of a spar-type wind turbine known as the OC3-Hywind concept and the dynamic responses of the turbine. Response characteristics of motions and mooring loads of the system under different sea states are evaluated and the effects of the loads induced by the wind and the wave on the system are discussed. The calculations are carried out with the numerical simulation code FAST in the time domain and the frequency analysis is made by using the FFT method. The results and the conclusions from this paper might help better understand the behavior characteristics of the floating wind turbine system under actual ocean environments and provide valuable data in design and engineering practice.
42 citations
TL;DR: In this article, the authors assess the suitable parameterization of woody riparian vegetation in estimating the drag forces, and evaluate the applicability of three recently developed flow resistance models.
Abstract: To reliably estimate water levels and velocities in vegetated rivers and floodplains, flow resistance models based on physical plant properties are advantageous. The purpose of this study is (1) to assess the suitable parameterization of woody riparian vegetation in estimating the drag forces, (2) to address the effect of plant scale on the drag estimates and reconfiguration, and (3) to evaluate the applicability of three recently developed flow resistance models. Experiments on four tree species in a towing tank together with detailed characterization of tree properties were carried out to establish a novel dataset. Despite the variability in the tree height (0.9 m–3.4 m), the stem, leaf and total areas proved to be suitable characteristic dimensions for estimating the flow resistance at different scales. Evaluations with independent data revealed that the tested models produced reasonable results. The performance of the models was controlled by the parameter values used rather than the model structure or the plant scale.
42 citations
TL;DR: In this article, a simulation of a pump rising pipeline system with an air chamber was performed to simulate the hydraulic transient response to tripping of a set of pumps, which can lead to overpressure and negative pressure.
Abstract: Water hammer following the tripping of pumps can lead to overpressure and negative pressure. Reduction in overpressure and negative pressure may be necessary to avoid failure, to improve the efficiency of operation and to avoid fatigue of system components. The field tests on the water hammer have been conducted on the pump rising pipeline system with an air chamber. The hydraulic transient was simulated using the method of characteristics. Minimizing the least squares problem representing the difference between the measured and predicted transient response in the system performs the calibration of the simulation program. Among the input variables used in the water hammer analysis, the polytropic exponent, the discharge coefficient and the wave speed were calibrated. The computer program developed in this study will be useful in designing the optimum parameters of an air chamber for the real pump pipeline system. The correct selection of air chamber size and the effect of the inner diameter of the orifice to minimize water hammer have been investigated by both field measurements and numerical modeling.
37 citations
TL;DR: In this paper, a prediction method for the natural gas hydrate formation region during the deep-water gas well testing is proposed, which combines the wellbore temperature field equations, the phase equilibrium conditions of the natural gaseous formation and the calculation methods for the pressure field.
Abstract: Wellbore temperature field equations are established with considerations of the enthalpy changes of the natural gas during the deep-water gas well testing. A prediction method for the natural gas hydrate formation region during the deep-water gas well testing is proposed, which combines the wellbore temperature field equations, the phase equilibrium conditions of the natural gas hydrate formation and the calculation methods for the pressure field. Through the sensitivity analysis of the parameters that affect the hydrate formation region, it can be concluded that during the deep-water gas well testing, with the reduction of the gas production rate and the decrease of the geothermal gradient, along with the increase of the depth of water, the hydrate formation region in the wellbore enlarges, the hydrate formation regions differ with different component contents of natural gases, as compared with the pure methane gas, with the increase of ethane and propane, the hydrate formation region expands, the admixture of inhibitors, the type and the concentrations of which can be optimized through the method proposed in the paper, will reduce the hydrate formation region, the throttling effect will lead to the abrupt changes of temperature and pressure, which results in a variation of the hydrate formation region, if the throttling occurs in the shallow part of the wellbore, the temperature will drop too much, which enlarges the hydrate formation region, otherwise, if the throttling occurs in the deep part of the wellbore, the hydrate formation region will be reduced due to the decrease of the pressure.
TL;DR: An integrated hydrodynamic computational tool that consists of a potential-flow based simple CFD tool and an Euler/RANS/Navier-Stokes based advancedCFD tool has been further developed and integrated into a practical multiobjective hydrod dynamic optimization tool.
Abstract: A new methodology for hydrodynamic optimization of a TriSWACH is developed, which considers not only the positions of the side hulls but also the shape of the side hulls. In order to account for the strong near-field interference effects between closely-spaced multihulls, an integrated hydrodynamic computational tool that consists of a potential-flow based simple CFD tool and an Euler/RANS/Navier-Stokes based advanced CFD tool has been further developed and integrated into a practical multi-objective hydrodynamic optimization tool. The other components of this hydrodynamic optimization tool consist of a hull shape representation and modification module and an optimization module. This enhanced multi-objective hydrodynamic optimization tool has been applied to the hydrodynamic design optimization of the TriSWACH for reduced drag by optimizing the side hulls only. A new methodology is developed to optimize side hull forms so that the TriSWACH has a minimal drag for a wide speed range and for various side hull positions. Two sets of the side hulls are developed and used for the design of two optimal TriSWACH models. Model tests are carried out for two optimal TriSWACH models at Webb Institute for validations. Substantial drag reductions have been obtained for a wide range of speed.
TL;DR: In this paper, the influence of hydrate phase transition on gas kick hydraulics is investigated through numerical simulations and it is shown that the diameter of the gas bubbles can significantly influence the hydrate phases transition effect.
Abstract: The hydrate phase transition presents new problems and challenges for the deepwater well control in the drilling processes. A simulation model is built for deepwater gas kicks with consideration of the hydrate phase transition. The model is based on the multiphase flow governing equations and the hydrate phase transition calculation equations. The influence of the hydrate phase transition on the gas kick hydraulics is investigated through numerical simulations. It is shown that the diameter of the gas bubbles can significantly influence the hydrate phase transition effect. The influence of the hydrate phase transition on the gas kick hydraulics increases with the decrease of the average gas bubble diameter. The hydrate phase transition adds a “hidden” nature for the well kick in deepwater and hinders the early detection of the gas kick. The influence of the hydrate phase transition on the gas kick hydraulics is also studied in the case when the hydrate inhibitor is added to the drilling fluid.
TL;DR: An overview of hydrodynamic problems related to the broad variety of ships and sea structures involved in transportation, oil and gas exploration and production, marine operations, recovery of oil-spill, renewable energy, infrastructure and aquaculture is given in this paper.
Abstract: An overview of hydrodynamic problems related to the broad variety of ships and sea structures involved in transportation, oil and gas exploration and production, marine operations, recovery of oil-spill, renewable energy, infrastructure and aquaculture is given. An approximate hydroelastic model for wave and current induced response of a floating fish farm with circular plastic collar and net cage is discussed. Weakly nonlinear potential-flow problems such as slow-drift motions and stationkeeping, springing of ships and ringing are given special attention. Body-fixed coordinate system is recommended in weakly nonlinear potential-flow analysis of bodies with sharp corners. Dynamic ship instabilities, Mathieu-type instabilities, chaos and two-phase flow involving interface instabilities are discussed. It is advocated that slamming must be coupled with structural mechanics in order to find important time scales of the many physical effects associated with slamming and that both water entry and exit matter in describing the global wetdeck slamming effects. Further, sloshing-induced slamming in prismatic LNG tanks is perhaps the most complicated slamming problem because many fluid mechanic and thermodynamic parameters as well as hydroelasticity may matter.
TL;DR: In this paper, the authors extended previous experimental and numerical analyses of the pressure pulse characteristics in a Francis turbine by using the unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) turbulence model to model the unstable flow within the entire flow passage of a large pump turbine with misaligned guide vanes at the rated rotational speed.
Abstract: Previous experimental and numerical analyses of the pressure pulse characteristics in a Francis turbine are extended here by using the unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) turbulence model to model the unsteady flow within the entire flow passage of a large Francis pump turbine with misaligned guide vanes at the rated rotational speed. The S-curve characteristics are analyzed by a combined use of the model test and the steady state simulation with the aligned guide vane firstly. Four misaligned guide vanes with two different openings are chosen to analyze the influence of pressure pulses in the turbine. The characteristics of the dominant unsteady flow frequencies in different parts of the pump turbine for various misaligned guide vane openings are investigated in detail. The predicted hydraulic performance and the pressure fluctuations show that the misaligned guide vanes reduce the relative pressure fluctuation amplitudes in the stationary part of the flow passage, but not the runner blades. The misaligned guide vanes have changed the low frequencies in the entire flow passage with the change of the pulse amplitudes mainly due to changes in the rotor-stator interaction and the low frequency vortex rope flow behavior.
TL;DR: To investigate the dynamic characteristics of the thermal conditions of hot-water district-heating networks, a dynamic modeling method is proposed with consideration of the heat dissipations in pipes and the characteristic line method is adopted to solve it.
Abstract: To investigate the dynamic characteristics of the thermal conditions of hot-water district-heating networks, a dynamic modeling method is proposed with consideration of the heat dissipations in pipes and the characteristic line method is adopted to solve it. Besides, the influences of different errors, space steps and initial values on the convergence of the dynamic model results are analyzed for a model network. Finally, a part of a certain city district-heating system is simulated and the results are compared with the actual operation data in half an hour from 6 secondary heat stations. The results indicate that the relative errors for the supply pressure and temperature in 5 stations are all within 2%, except in one station, where the relative error approaches 4%. So the proposed model and algorithm are validated.
TL;DR: In this paper, numerical prediction of ship motion responses in long-crest irregular waves by the URANS-VOF method is presented, where a white noise spectrum is applied to generate the incoming waves to evaluate the motion responses.
Abstract: In this paper, numerical prediction of ship motion responses in long-crest irregular waves by the URANS-VOF method is presented. A white noise spectrum is applied to generate the incoming waves to evaluate the motion responses. The procedure can replace a decade of simulations in regular wave with one single run to obtain a complete curve of linear motion response, considerably reducing computation time. A correction procedure is employed to adjust the wave generation signal based on the wave spectrum and achieves fairly better results in the wave tank. Three ship models with five wave conditions are introduced to validate the method. The computations in this paper are completed by using the solver naoe-FOAM-SJTU, a solver developed for ship and ocean engineering based on the open source code Open FOAM. The computational motion responses by the irregular wave procedure are compared with the results by regular wave, experiments and strip theory. Transfer functions by irregular wave closely agree with the data obtained in the regular waves, showing negligible difference. The comparison between computational results and experiments also show good agreements. The results better predicted by CFD method than strip theories indicate that this method can compensate for the inaccuracy of the strip theories. The results confirm that the irregular wave procedure is a promising method for the accurate prediction of motion responses with less accuracy loss and higher efficiency compared with the regular wave procedure.
TL;DR: In this article, the axial vortex is identified between impeller hub and guide vane hub, which is developed into the main flow and to affect the movement when the relative positions of impeller and vane at different flow rates are the same.
Abstract: Axial flow pump is a kind of typical pumps with rotor-stator interaction, thus the measurement of the flow field between impeller and guide vane would facilitate the study of the internal rotor-stator interaction mechanism. Through a structural modification of a traditional axial flow pump, the requirements of particle image velocimetry (PIV) measurement are met. Under the condition of 0.8 Q opt , the axial vortex is identified between impeller hub and guide vane hub, which is developed into the main flow and to affect the movement when the relative positions of impeller and guide vane at different flow rates are the same. Besides, the development and the dissipation of the tip leakage and the passage vortex in impeller passages are mainly responsible for the difference of the flow field close to the outer rim. As the flow rate decreases, the distribution of the meridional velocities at the impeller outlet becomes more non-uniform and the radial velocity component keeps increasing. The PIV measurement results under the condition of 1.0 Q opt indicate that the flow separation and the trailing vortex at the trailing edge of a blade are likely to result in a velocity sudden change in this area, which would dramatically destroy the continuity of the flow field. Moreover, the radial direction of the flow between impeller and guide vane on the measurement plane does not always point from hub to rim. For a certain position, the direction is just from rim to hub, as is affected by the location of the intersection line of the shooting section and the impeller blade on the impeller as well as the angle between the intersection line and the rotating shaft.
TL;DR: In this paper, numerical simulation and 3D periodic flow unsteadiness analysis for a centrifugal pump with volute are carried out in whole flow passage, including the impeller with twisted blades, the volute and the side chamber channels under a part-load condition.
Abstract: Numerical simulation and 3-D periodic flow unsteadiness analysis for a centrifugal pump with volute are carried out in whole flow passage, including the impeller with twisted blades, the volute and the side chamber channels under a part-load condition. The pressure fluctuation intensity coefficient (PFIC) based on the standard deviation method, the time-averaged velocity unsteadi- ness intensity coefficient (VUIC) and the time-averaged turbulence intensity coefficient (TIC) are defined by averaging the results at each grid node for an entire impeller revolution period. Therefore, the strength distributions of the periodic flow unsteadiness based on the unsteady Reynolds-averaged Navier-Stokes (URANS) equations can be analyzed directly and in detail. It is shown that under the 0.6 Q des. condition, the pressure fluctuation intensity is larger near the blade pressure side than near the suction side, and a high fluctuation intensity can be observed at the beginning section of the spiral of the volute. The flow velocity unsteadiness intensity is larger near the blade suction side than near the pressure side. A strong turbulence intensity can be found near the blade suction side, the impeller shroud side as well as in the side chamber. The leakage flow has a significant effect on the inflow of the impeller, and can increase both the flow velocity unsteadiness intensity and the turbulence intensity near the wall. The accumulative flow unstea- diness results of an impeller revolution can be an important aspect to be considered in the centrifugal pump optimum design for ob- taining a more stable inner flow of the pump and reducing the flow-induced vibration and noise in certain components.
TL;DR: In this paper, the in-house multifunction solver naoe-FOAM-SJTU is applied to study the resistance and wave-making performance of a high-speed catamaran sailing at different velocity in calm water.
Abstract: In this paper, the in-house multifunction solver naoe-FOAM-SJTU is applied to study the resistance and wave-making performance of a high-speed catamaran sailing at different velocity in calm water. The volume of fluid (VOF) method is used to capture the free interface and the finite volume method (FVM) is adopted as the discretization scheme. The hull model is fixed with initial trim and sinkage. The numerical results of the presented paper agree very well with the measurement data of model test. Wave making and vortex field are well simulated to analyze the hydrodynamic performance of a catamaran.
TL;DR: In this paper, a hybrid scheme coupling the discrete element method (DEM) with the computational fluid dynamics (CFD) is developed to model solid-liquid flows, where instead of solving the pressure Poisson equation, they use the compressible volume-averaged continuity and momentum equations with an isothermal stiff equation of state for the liquid phase in their scheme.
Abstract: A hybrid scheme coupling the discrete element method (DEM) with the computational fluid dynamics (CFD) is developed to model solid-liquid flows. Instead of solving the pressure Poisson equation, we use the compressible volume-averaged continuity and momentum equations with an isothermal stiff equation of state for the liquid phase in our CFD scheme. The motion of the solid phase is obtained by using the DEM, in which the particle-particle and particle-wall interactions are modelled by using the theoretical contact mechanics. The two phases are coupled through the Newton's third law of motion. To verify the proposed method, the sedimentation of a single spherical particle is simulated in water, and the results are compared with experimental results reported in the literature. In addition, the drafting, kissing, and tumbling (DKT) phenomenon between two particles in a liquid is modelled and reasonable results are obtained. Finally, the numerical simulation of the density-driven segregation of a binary particulate suspension involving 10 000 particles in a closed container is conducted to show that the presented method is potentially powerful to simulate real particulate flows with large number of moving particles.
TL;DR: In this article, the authors analyzed the sediment siltation in the upper reach of the Deepwater Navigation Channel Project in the Yangtze Estuary after the project has been implemented.
Abstract: The results from both the field measurements and numerical simulation were reported to comprehensively analyze the sediment siltation in the upper reach of the Deepwater Navigation Channel Project in the Yangtze Estuary after the project has been implemented. In this research, firstly some basic information about the river evolution in the Yangtze Estuary is analyzed, including the variations of water depths in the Hengsha Passage and the inlet cross-sections of the North Passage and the South Passage, and changes of diversion ratios of ebb flow and sediment flux in the North Passage and the South Passage. Then the Delft3D-FLOW model is applied to simulate the hydrodynamics and sediment transport in the Yangtze Estuary. This model has been calibrated and the simulated results agree well with the measured data of the tidal levels, flow velocities and suspended sediment concentration (SSC), indicating that the model can well simulate the hydrodynamics and sediment transport of the Yangtze Estuary caused by the Deepwater Navigation Channel Project. The research results show that the development of the Hengsha Passage and decrease of diversion ratio of ebb flow and sediment flux in the North Passage are the main reasons of sediment siltation in the upper reach of the Deepwater Navigation Channel in the Yangtze Estuary.
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TL;DR: A Boundary Element Method (BEM) hydrodynamics combined with a flow-alignment technique to evaluate blades shed vorticity is presented and applied to a marine propeller in open water as discussed by the authors.
Abstract: A Boundary Element Method (BEM) hydrodynamics combined with a flow-alignment technique to evaluate blades shed vorticity is presented and applied to a marine propeller in open water. Potentialities and drawbacks of this approach in capturing propeller performance, slipstream velocities, blade pressure distribution and pressure disturbance in the flow-field are highlighted by comparisons with available experiments and RANSE results. In particular, correlations between the shape of the convected vortex- sheet and the accuracy of BEM results are discussed throughout the paper. To this aim, the analysis of propeller thrust and torque is the starting point towards a detailed discussion on the capability of a 3-D free-wake BEM hydrodynamic approach to describe the local features of the flow-field behind the propeller disk, in view of applications to propulsive configurations where the shed wake plays a dominant role.
TL;DR: Wang et al. as discussed by the authors studied the influences of hydraulic and mechanical parameters on land subsidence and ground fissure caused by groundwater exploitation, based on the Biot's consolidation theory and combined with the nonlinear rheological theory of soil.
Abstract: In order to study the influences of hydraulic and mechanical parameters on land subsidence and ground fissure caused by groundwater exploitation, based on the Biot’s consolidation theory and combined with the nonlinear rheological theory of soil, the constitutive relation in Biot’s consolidation theory is extended to include the viscoelastic plasticity, and the dynamic relationship among the porosity, the hydraulic conductivity, the parameters of soil deformation and effective stress is also considered, a threedimensional full coupling mathematical model is established and applied to the study of land subsidence and ground fissures of Cangzhou in Hebei Province, through the analysis of parameter sensitivity, the influences of soil hydraulic and mechanical parameters on land subsidence and ground fissure are revealed. It is shown that the elastic modulus E, the Poisson ratio ν, the specific yield μ and the soil cohesion c have a great influence on the land subsidence and the ground fissures. In addition, the vertical hydraulic conductivity k
z and the horizontal hydraulic conductivity k
z also have a great influence on the land subsidence and the ground fissures.
TL;DR: In this paper, a fully implicit reservoir simulator is developed for the optimization of the injection-production rate of water-oil wells in a complex oil-gas filtration system.
Abstract: The oil recovery enhancement is a major technical issue in the development of oil and gas fields. The smart oil field is an effective way to deal with the issue. It can achieve the maximum profits in the oil production at a minimum cost, and represents the future direction of oil fields. This paper discusses the core of the smart field theory, mainly the real-time optimization method of the injection-production rate of water-oil wells in a complex oil-gas filtration system. Computing speed is considered as the primary prerequisite because this research depends very much on reservoir numerical simulations and each simulation may take several hours or even days. An adjoint gradient method of the maximum theory is chosen for the solution of the optimal control variables. Conventional solving method of the maximum principle requires two solutions of time series: the forward reservoir simulation and the backward adjoint gradient calculation. In this paper, the two processes are combined together and a fully implicit reservoir simulator is developed. The matrixes of the adjoint equation are directly obtained from the fully implicit reservoir simulation, which accelerates the optimization solution and enhances the efficiency of the solving model. Meanwhile, a gradient projection algorithm combined with the maximum theory is used to constrain the parameters in the oil field development, which make it possible for the method to be applied to the water flooding optimization in a real oil field. The above theory is tested in several reservoir cases and it is shown that a better development effect of the oil field can be achieved.
TL;DR: In this article, a detailed study of the temperature and pressure distributions of the supercritical carbon dioxide (SC-CO 2 ) jet on the bottom of a well is performed, and the impacts of the nozzle diameter, the jet length and the inlet pressure of the SC-CO2 jet are analyzed.
Abstract: The supercritical carbon dioxide (SC-CO 2 ) drilling is a novel drilling technique developed in recent years. A detailed study of temperature and pressure distributions of the SC-CO 2 jet on the bottom of a well is essensial to the SC-CO 2 drilling. In this paper, the distributions of pressure and temperature on the bottom of the hole during the SC-CO 2 jet drilling are simulated experimentally and numerically, and the impacts of the nozzle diameter, the jet length, and the inlet pressure of the SC-CO 2 jet are analyzed. It is shown that, the bottom hole temperature and pressure increase with the increase of the nozzle diameter, and the bottom hole temperature reduces and the pressure increases first and then decreases with the increase of the jet length, indicating that the jet length has an optimum value. The increase of the inlet pressure can increase the temperature and pressure on the bottom, which has a positive effect on the drilling rate.
TL;DR: In this article, the impact of rough ice cover roughness on the scour geometry around the semi-circular abutment of a bridge was investigated and the maximum scour depth was located 75° inclined to the flume wall.
Abstract: The presence of ice cover in winter can significantly change the flow field around bridge abutments, which can also cause a different local scour pattern To investigate the impacts of ice cover, results from a recent flume experiments were presented Smooth and rough ice covers were created to investigate the impacts of ice cover roughness on the scour geometry around the semi-circular abutment Three bed materials were used, with D 50 S of 058 mm, 050 mm, 047 mm respectively Scour volume and scour area were calculated It was found that the maximum scour depth was located 75° inclined to the flume wall Under rough ice cover, the scour area and scour depth were the largest An empirical equation on the maximum scour depth was also developed
TL;DR: In this paper, a tree-shaped fractal network is used to simulate a fracture network and a Laplace-convolutional model is proposed to predict the pressure dynamic characteristics of naturally fractured reservoirs.
Abstract: A transient flow model of tree-shaped fractal reservoirs is built by embedding a fracture network simulated by a tree-shaped fractal network into a matrix system. The model can be solved using the Laplace conversion method. The dimensionless bottom hole pressure can be obtained using the Stehfest numerical inversion method. The bi-logarithmic type curves for the tree-shaped fractal reservoirs are thus obtained. The pressure transient responses under different fractal factors are discussed. The factors with a primary effect on the inter-porosity flow regime include the initial branch number N , the length ratio α, and the branch angle θ. The diameter ratio β has a significant effect on the fracture radial flow, the inter-porosity and the total system radial flow regimes. The total branch level M of the network mainly influences the total system radial flow regime. The model presented in this paper provides a new methodology for analyzing and predicting the pressure dynamic characteristics of naturally fractured reservoirs.
TL;DR: In this article, the migration mechanism of the base soil through this type of filters with a fluid flow was studied by using the coupled distinct element method and computational fluid dynamics (DEM-CFD) model and the time-dependent variations of the system parameters such as the total eroded base soil mass, the distribution of the eroded particles within the filter, the porosity, the pore water pressure, and the flow discharge were obtained and analyzed.
Abstract: In embankments and earth dams, the granular filter used to protect the base soil from being eroded by the fluid flow is a major safety device. In this paper, the migration mechanism of the base soil through this type of filters with a fluid flow in the base soil-filter system is studied by using the coupled distinct element method and computational fluid dynamics (DEM-CFD) model. The time-dependent variations of the system parameters such as the total eroded base soil mass, the distribution of the eroded particles within the filter, the porosity, the pore water pressure, and the flow discharge are obtained and analyzed. The conceptions of the trapped particle and the trapped ratio are proposed in order to evaluate the trapped condition of the base soil particles in the filter. The variation of the trapped ratio with time is also analyzed. The results show that the time evolutions of the parameters mentioned above are directly related to the gradation of the filter, which is defined as the representative particle size ratio of the base soil to the filter using an empirical filter design criterion. The feasibility of the model is validated by comparing the numerical results with some experimental and numerical results.
TL;DR: In this paper, a numerical simulation is carried out based on a RANS-VOF solver to analyze the hydrodynamic performance of a channel type planing trimaran.
Abstract: This paper studies the hydrodynamic performance of a channel type planing trimaran. A numerical simulation is carried out based on a RANS-VOF solver to analyze the hydrodynamic performance of the channel type planing trimaran. A series of hydrodynamic experiments in towing tank were carried out, in which both the running attitude and the resistance performance of the trimaran model were recorded. Some hydrodynamic characteristics of the channel type planning trimaran are shown by the results. Firstly, the resistance declines significantly, with the forward speed across the high-speed resistance peak due to the combined effects of the aerodynamic and hydrodynamic lifts. Secondly, the resistance performance is influenced markedly by the longitudinal positions of centre of the gravity and the displacements. Besides, the pressure distribution on the hull and the two-phase flow in the channel are discussed in the numerical simulations.