Semisubmersible naval ships are versatile military crafts that combine the advantageous features of high-speed planing crafts and submarines.At-surface,these ships are designed to provide sufficient speed and maneuver...Semisubmersible naval ships are versatile military crafts that combine the advantageous features of high-speed planing crafts and submarines.At-surface,these ships are designed to provide sufficient speed and maneuverability.Additionally,they can perform shallow dives,offering low visual and acoustic detectability.Therefore,the hydrodynamic design of a semisubmersible naval ship should address at-surface and submerged conditions.In this study,Numerical analyses were performed using a semisubmersible hull form to analyze its hydrodynamic features,including resistance,powering,and maneuvering.The simulations were conducted with Star CCM+version 2302,a commercial package program that solves URANS equations using the SST k-ωturbulence model.The flow analysis was divided into two parts:at-surface simulations and shallowly submerged simulations.At-surface simulations cover the resistance,powering,trim,and sinkage at transition and planing regimes,with corresponding Froude numbers ranging from 0.42 to 1.69.Shallowly submerged simulations were performed at seven different submergence depths,ranging from D/LOA=0.0635 to D/LOA=0.635,and at two different speeds with Froude numbers of 0.21 and 0.33.The behaviors of the hydrodynamic forces and pitching moment for different operation depths were comprehensively analyzed.The results of the numerical analyses provide valuable insights into the hydrodynamic performance of semisubmersible naval ships,highlighting the critical factors influencing their resistance,powering,and maneuvering capabilities in both at-surface and submerged conditions.展开更多
The main ideas in the development of the solvent extraction mixer settler focused on achieving clean phase separation,minimizing the loss of the reagents and decreasing the surface area of the settlers.The role of baf...The main ideas in the development of the solvent extraction mixer settler focused on achieving clean phase separation,minimizing the loss of the reagents and decreasing the surface area of the settlers.The role of baffles in a mechanically agitated vessel is to ensure even distribution,reduce settler turbulence,promote the stability of power drawn by the impeller and to prevent swirling and vortexing of liquid,thus,greatly improving the mixing of liquid.The insertion of the appropriate number of baffles clearly improves the extent of liquid mixing.However,excessive baffling would interrupt liquid mixing and lengthen the mixing time.Computational fluid dynamics(CFD) provides a tool for determining detailed information on fluid flow(hydrodynamics) which is necessary for modeling subprocesses in mixer settler.A total of 54 final CFD runs were carried out representing different combinations of variables like number of baffles,density and impeller speed.CFD data shows that amount of separation increases with increasing baffles number and decreasing impeller speed.展开更多
This paper presents a time-efficient numerical approach to modelling high explosive(HE)blastwave propagation using Computational Fluid Dynamics(CFD).One of the main issues of using conventional CFD modelling in high e...This paper presents a time-efficient numerical approach to modelling high explosive(HE)blastwave propagation using Computational Fluid Dynamics(CFD).One of the main issues of using conventional CFD modelling in high explosive simulations is the ability to accurately define the initial blastwave properties that arise from the ignition and consequent explosion.Specialised codes often employ Jones-Wilkins-Lee(JWL)or similar equation of state(EOS)to simulate blasts.However,most available CFD codes are limited in terms of EOS modelling.They are restrictive to the Ideal Gas Law(IGL)for compressible flows,which is generally unsuitable for blast simulations.To this end,this paper presents a numerical approach to simulate blastwave propagation for any generic CFD code using the IGL EOS.A new method known as the Input Cavity Method(ICM)is defined where input conditions of the high explosives are given in the form of pressure,velocity and temperature time-history curves.These time history curves are input at a certain distance from the centre of the charge.It is shown that the ICM numerical method can accurately predict over-pressure and impulse time history at measured locations for the incident,reflective and complex multiple reflection scenarios with high numerical accuracy compared to experimental measurements.The ICM is compared to the Pressure Bubble Method(PBM),a common approach to replicating initial conditions for a high explosive in Finite Volume modelling.It is shown that the ICM outperforms the PBM on multiple fronts,such as peak values and overall overpressure curve shape.Finally,the paper also presents the importance of choosing an appropriate solver between the Pressure Based Solver(PBS)and Density-Based Solver(DBS)and provides the advantages and disadvantages of either choice.In general,it is shown that the PBS can resolve and capture the interactions of blastwaves to a higher degree of resolution than the DBS.This is achieved at a much higher computational cost,showing that the DBS is much preferred for quick turnarounds.展开更多
Computational fluid dynamics （CFD） plays a major role in predicting the flow behavior of a ship. With the development of fast computers and robust CFD software, CFD has become an important tool for designers and eng...Computational fluid dynamics （CFD） plays a major role in predicting the flow behavior of a ship. With the development of fast computers and robust CFD software, CFD has become an important tool for designers and engineers in the ship industry. In this paper, the hull form of a ship was optimized for total resistance using CFD as a calculation tool and a genetic algorithm as an optimization tool. CFD based optimization consists of major steps involving automatic generation of geometry based on design parameters, automatic generation of mesh, automatic analysis of fluid flow to calculate the required objective/cost function, and finally an optimization tool to evaluate the cost for optimization. In this paper, integration of a genetic algorithm program, written in MATLAB, was carried out with the geometry and meshing software GAMBIT and CFD analysis software FLUENT. Different geometries of additive bulbous bow were incorporated in the original hull based on design parameters. These design variables were optimized to achieve a minimum cost function of ＂total resistance＂. Integration of a genetic algorithm with CFD tools proves to be effective for hull form ootimization.展开更多
A three-dimensional model for gas-solid flow in a circulating fluidized bed（CFB） riser was developed based on computational particle fluid dynamics（CPFD）.The model was used to simulate the gas-solid flow behavior ...A three-dimensional model for gas-solid flow in a circulating fluidized bed（CFB） riser was developed based on computational particle fluid dynamics（CPFD）.The model was used to simulate the gas-solid flow behavior inside a circulating fluidized bed riser operating at various superficial gas velocities and solids mass fluxes in two fluidization regimes,a dilute phase transport（DPT） regime and a fast fluidization（FF） regime.The simulation results were evaluated based on comparison with experimental data of solids velocity and holdup,obtained from non-invasive automated radioactive particle tracking and gamma-ray tomography techniques,respectively.The agreement of the predicted solids velocity and holdup with experimental data validated the CPFD model for the CFB riser.The model predicted the main features of the gas-solid flows in the two regimes;the uniform dilute phase in the DPT regime,and the coexistence of the dilute phase in the upper region and the dense phase in the lower region in the FF regime.The clustering and solids back mixing in the FF regime were stronger than those in the DPT regime.展开更多
We investigated the effect of supply air rate and temperature on formaldehyde emission characteristics in an environment chamber.A three-dimensional computational fluid dynamics(CFD) chamber model for simulating forma...We investigated the effect of supply air rate and temperature on formaldehyde emission characteristics in an environment chamber.A three-dimensional computational fluid dynamics(CFD) chamber model for simulating formaldehyde emission in twelve different cases was developed for obtaining formaldehyde concentration by the area-weighted average method.Laboratory experiments were conducted in an environment chamber to validate the simulation results of twelve different cases and the formaldehyde concentration was measured by continuous sampling.The results show that there was good agreement between the model prediction and the experimental values within 4.3 difference for each case.The CFD simulation results varied in the range from 0.21 mg/m3 to 0.94 mg/m3,and the measuring results in the range from 0.17 mg/m3 to 0.87 mg/m3.The variation trend of formaldehyde concentration with supply air rate and temperature variation for CFD simulation and experiment measuring was consistent.With the existence of steady formaldehyde emission sources,formaldehyde concentration generally increased with the increase of temperature,and it decreased with the increase of air supply rate.We also provided some reasonable suggestions to reduce formaldehyde concentration and to improve indoor air quality for newly decorated rooms.展开更多
This work proposes a vibrating mesh screen as an alternative to the static mesh screen currently used in conventional flooded-bed dust scrubbers for removing airborne coal mine dust in the continuous mining environmen...This work proposes a vibrating mesh screen as an alternative to the static mesh screen currently used in conventional flooded-bed dust scrubbers for removing airborne coal mine dust in the continuous mining environment.Fundamental assessments suggest that a vibrating screen may improve the dust collection efficiency of scrubber systems and mitigate the clogging issues associated with the conventional design.To evaluate this hypothesis,computational fluid dynamics(CFD)simulations were carried out to assess the effects of vibration conditions(i.e.,frequency and amplitude)on the dust particle-mesh interaction and mesh wetting conditions,which are the two decisive factors in determining the dust collection efficiency.The results suggest that the vibrating mesh screen can enhance dust particle collision opportunities on the mesh and increase mesh wetted area as compared to the static mesh screen.The effects of mesh screen aperture,coal dust concentration,and spray nozzle flow rate on the performance of the vibrating mesh are also evaluated.Finally,a simplified three-phase flow simulation including airflow,dust particles,and water droplet spray is performed,and the results reflect a significant improvement of dust collection efficiency in the liquid-coated vibrating mesh screen.展开更多
The computational fluid dynamics(CFD) code, FLUENT, was used to simulate the liquid-phase FCC diesel hydrotreating tubular reactor with a ceramic membrane tube dispenser. The chemical reaction and reaction heat were a...The computational fluid dynamics(CFD) code, FLUENT, was used to simulate the liquid-phase FCC diesel hydrotreating tubular reactor with a ceramic membrane tube dispenser. The chemical reaction and reaction heat were added to the model by user-defined function(UDF), showing the distribution of temperature and content of sulfides, nitrides, bicyclic aromatics and monocyclic aromatics in different parts of the reaction bed. When the pressure was 6.5 MPa, the amount of mixing hydrogen was 0.84%(m), the space velocity was 2 h-1 and the inlet temperature was 633 K, the temperature reached a maximum at a height of 0.15 m, and the range of radial temperature reached its maximum(2.5 K) at a height of 0.15 m. It indicated that the proper ratio of height to diameter of catalyst bed in the tubular reactor was 5-6. The increase of inlet temperature, the mixing hydrogen and the decrease of space velocity led to the decrease in the content of bicyclic aromatics, sulfides and nitrides, and the increase in monocyclic aromatics content, while the high temperature increased. The results were in good agreement with experimental data, indicating to the high accuracy of the model.展开更多
Three-dimensional compressible flow simulationswere conducted to develop a Hyperloop pod. Thenovelty is the usage of Gamma transition model, in whichthe transition from laminar to turbulent flow can be predicted.First...Three-dimensional compressible flow simulationswere conducted to develop a Hyperloop pod. Thenovelty is the usage of Gamma transition model, in whichthe transition from laminar to turbulent flow can be predicted.First, a mesh dependency study was undertaken,showing second-order convergence with respect to themesh refinement. Second, an aerodynamic analysis for twodesigns, short and optimized, was conducted with thetraveling speed 125 m/s at the system pressure 0.15 bar.The concept of the short model was to delay the transitionto decrease the frictional drag;meanwhile that of theoptimized design was to minimize the pressure drag bydecreasing the frontal area and introduce the transitionmore toward the front of the pod. The computed resultsshow that the transition of the short model occurred moreon the rear side due to the pod shape, which resulted in 8%smaller frictional drag coefficient than that for the optimizedmodel. The pressure drag for the optimized designwas 24% smaller than that for the short design, half ofwhich is due to the decrease in the frontal area, and theother half is due to the smoothed rear-end shape. The totaldrag for the optimized model was 14% smaller than that forthe short model. Finally, the influence of the systempressure was investigated. As the system pressure and theReynolds number increase, the frictional drag coefficientincreases, and the transition point moves toward the front,which are the typical phenomena observed in the transitionregime.展开更多
Metal organic chenlical vapor deposition （AIOCVD） growth systems arc one of the. main types of equipment used for growing single crystal materials, such as GaN. To obtain fihn epitaxial materials with uniform perfor...Metal organic chenlical vapor deposition （AIOCVD） growth systems arc one of the. main types of equipment used for growing single crystal materials, such as GaN. To obtain fihn epitaxial materials with uniform performanee, the flow field and ternperature field in a GaN-MOCVD reactor are investigated by modeling and simulating. To make the simulation results more consistent with the actual situation, the gases in the reactor are considered to be compressible, making it possible to investigate the distributions of gas density and pressure in the reactor. The computational fluid dynamics method is used to stud,v the effects of inlet gas flow velocity, pressure in the reactor, rotational speed of graphite susceptor, and gases used in the growth, which has great guiding~ significance for the growth of GaN fihn materials.展开更多
Left ventricular assist device( LVAD) in this study is a mechanical tool that is used to support blood flow in the patient with heart disease. It supports left ventricle by building up the pressure to the pump outlet ...Left ventricular assist device( LVAD) in this study is a mechanical tool that is used to support blood flow in the patient with heart disease. It supports left ventricle by building up the pressure to the pump outlet connected to the aorta. This pump was designed based on the magnetic driven centrifugal pump with a unique small washout hole constructed inside the impeller to generate the washout flow passage to prevent the stagnation at the region underneath and around the rotor. Computational fluid dynamics( CFD) was adopted in this study to assess the performance and optimize the design to avoid recirculation and high shear stress which is the main cause of stagnation and blood damage. Transient simulation was used for this study due to the asymmetric design of the washout hole and the complication of the bottom support of the impeller that has a risk of thrombosis,also,it was used to predict the variation of hydraulic performance caused by the rotation of the impeller and pulsed flow at the pump inlet. The simulation results show no excessive stress and no recirculation observed within the computational domain; in addition,the research result also provides information for further optimization and development to the pump.展开更多
In Fluid Structure Interaction(FSI) problems encountered in marine hydrodynamics, the pressure field and the velocity of the rigid body are tightly coupled. This coupling is traditionally resolved in a partitioned man...In Fluid Structure Interaction(FSI) problems encountered in marine hydrodynamics, the pressure field and the velocity of the rigid body are tightly coupled. This coupling is traditionally resolved in a partitioned manner by solving the rigid body motion equations once per nonlinear correction loop, updating the position of the body and solving the fluid flow equations in the new configuration. The partitioned approach requires a large number of nonlinear iteration loops per time–step. In order to enhance the coupling, a monolithic approach is proposed in Finite Volume(FV) framework,where the pressure equation and the rigid body motion equations are solved in a single linear system. The coupling is resolved by solving the rigid body motion equations once per linear solver iteration of the pressure equation, where updated pressure field is used to calculate new forces acting on the body, and by introducing the updated rigid body boundary velocity in to the pressure equation. In this paper the monolithic coupling is validated on a simple 2D heave decay case. Additionally, the method is compared to the traditional partitioned approach(i.e. "strongly coupled" approach) in terms of computational efficiency and accuracy. The comparison is performed on a seakeeping case in regular head waves, and it shows that the monolithic approach achieves similar accuracy with fewer nonlinear correctors per time–step. Hence, significant savings in computational time can be achieved while retaining the same level of accuracy.展开更多
A numerical study of ship-to-ship interaction forces is performed using a commercial CFD code,and the results are compared with experimental data and with the results of a panel method analysis.Two ship models have be...A numerical study of ship-to-ship interaction forces is performed using a commercial CFD code,and the results are compared with experimental data and with the results of a panel method analysis.Two ship models have been used in the interaction forces analysis:a tug and a tanker,advancing parallel to each other with different lateral distances and two different values of the fluid depth.Computations are carried out with four different flow models:inviscid and viscous flow with the free surface modeled as a rigid wall and inviscid and viscous flow with the deformable free surface.A fair agreement was obtained with available experimental data and results obtained by panel method.The influence of viscosity in the computations is found to be comparatively weak,while the wavemaking effects may be important,at small magnitude of the horizontal clearance.展开更多
In the present paper,the hydrodynamic performance of stepped planing craft is investigated by computational fluid dynamics(CFD)analysis.For this purpose,the hydrodynamic resistances of without step,one-step,and two-st...In the present paper,the hydrodynamic performance of stepped planing craft is investigated by computational fluid dynamics(CFD)analysis.For this purpose,the hydrodynamic resistances of without step,one-step,and two-step hulls of Cougar planing craft are evaluated under different distances of the second step and LCG from aft,weight loadings,and Froude numbers(Fr).Our CFD results are appropriately validated against our conducted experimental test in National Iranians Marine Laboratory(NIMALA),Tehran,Iran.Then,the hydrodynamic resistance of intended planing crafts under various geometrical and physical conditions is predicted using artificial neural networks(ANNs).CFD analysis shows two different trends in the growth rate of resistance to weight ratio.So that,using steps for planing craft increases the resistance to weight ratio at lower Fr and decreases it at higher Fr.Additionally,by the increase of the distance between two steps,the resistance to weight ratio is decreased and the porpoising phenomenon is delayed.Furthermore,we obtained the maximum mean square error of ANNs output in the prediction of resistance to weight ratio equal to 0.0027.Finally,the predictive equation is suggested for the resistance to weight ratio of stepped planing craft according to weights and bias of designed ANNs.展开更多
Appropriate interaction between pantograph and catenary is imperative for smooth operation of electric trains.Changing heights of overhead lines to accommodate level crossings,overbridges,and tunnels pose significant ...Appropriate interaction between pantograph and catenary is imperative for smooth operation of electric trains.Changing heights of overhead lines to accommodate level crossings,overbridges,and tunnels pose significant challenges in maintaining consistent current collection performance as the pantograph aerodynamic profile,and thus aerodynamic load changes significantly with operational height.This research aims to analyse the global flow characteristics and aerodynamic forces acting on individual components of an HSX pantograph operating in different configurations and orientations,such that the results can be combined with multibody simulations to obtain accurate dynamic insight into contact forces.Specifically,computational fluid dynamics simulations are used to investigate the pantograph component loads in a representative setting,such as that of the recessed cavity on a Class 800 train.From an aerodynamic perspective,this study indicates that the total drag force acting on non-fixed components of the pantograph is larger for the knuckle-leading orientation rather than the knuckle-trailing,although the difference between the two is found to reduce with increasing pantograph extension.Combining the aerodynamic loads acting on individual components with multibody tools allows for realistic dynamic insight into the pantograph behaviour.The results obtained show how considering aerodynamic forces enhance the realism of the models,leading to behaviour of the pantograph-catenary contact forces closely matching that seen in experimental tests.展开更多
To simulate floating offshore wind turbine(FOWT)in coupled wind-wave domain via CFD method,the NREL 5MW wind turbine supported by the OC3-Hywind Spar platform is modeled in the STAR-CCM+ software.Based on the Reynolds...To simulate floating offshore wind turbine(FOWT)in coupled wind-wave domain via CFD method,the NREL 5MW wind turbine supported by the OC3-Hywind Spar platform is modeled in the STAR-CCM+ software.Based on the Reynolds-averaged Navier-Stokes(RANS)equations and re-normalisation group(RNG)k-εturbulence model,the rotor aerodynamic simulation for wind turbine is conducted.Numerical results agree well with the NREL data.Taking advantage with the volume of fluid(VOF)method and dynamic fluid body interaction(DFBI)technology,the dynamic responses of the floating system with mooring lines are simulated under the coupled wind-wave sea condition.The free-decay tests for rigid-body degrees of freedom(DOFs)in still water and hydrodynamic tests in a regular wave are performed to validate the numerical model by comparing its result with the results simulated by FAST.Finally,the simulations of the overall FOWT system in the coupled wind-wave flow field are carried out.The relationship between the power output and dynamic motion responses of the platform is investigated.The numerical results show that the dynamic response of wind turbine performance and platform motions all vary in the same frequency as the inlet wave.During platform motion,the power output of wind turbine is more sensitive than the thrust force.This study may provide some reference for further research in the coupled aero-hydro simulation of FOWT.展开更多
[Introduction] Accurate calculation of the hydrodynamic coefficients for floating structures and the investigation of the flow field distribution around floating bodies on the marine free surface are essential for imp...[Introduction] Accurate calculation of the hydrodynamic coefficients for floating structures and the investigation of the flow field distribution around floating bodies on the marine free surface are essential for improving the engineering design and application of marine structures.[Method] This study utilized the computational fluid dynamics(CFD) approach and the Reynolds Averaged NavierStokes(RANS) method and considered the effects of viscosity and free surface interactions on the hydrodynamic behavior of floating structures.By employing the dynamic mesh technique,this study simulated the periodic movements of simplified three-dimensional(3D)shapes:spheres,cylinders,and cubes,which were representative of complex marine structures.The volume of fluid(VOF) method was leveraged to accurately track the nonlinear behavior of the free surface.In this analysis,the added mass and damping coefficients for the fundamental modes of motion(surge,heave,and roll) were calculated across a spectrum of frequencies,facilitating the fast determination of hydrodynamic forces and moments exerted on floating structures.[Result] The results of this study are not only consistent with the results of the 3D potential flow theory but also further reflect the role of viscosity.This method can be used for precise calculation of the hydrodynamic coefficients of floating structures and for describing the flow field of such structures in motion on a free surface.[Conclusion] The methodology presented goes beyond the traditional potential flow approach.展开更多
文摘Semisubmersible naval ships are versatile military crafts that combine the advantageous features of high-speed planing crafts and submarines.At-surface,these ships are designed to provide sufficient speed and maneuverability.Additionally,they can perform shallow dives,offering low visual and acoustic detectability.Therefore,the hydrodynamic design of a semisubmersible naval ship should address at-surface and submerged conditions.In this study,Numerical analyses were performed using a semisubmersible hull form to analyze its hydrodynamic features,including resistance,powering,and maneuvering.The simulations were conducted with Star CCM+version 2302,a commercial package program that solves URANS equations using the SST k-ωturbulence model.The flow analysis was divided into two parts:at-surface simulations and shallowly submerged simulations.At-surface simulations cover the resistance,powering,trim,and sinkage at transition and planing regimes,with corresponding Froude numbers ranging from 0.42 to 1.69.Shallowly submerged simulations were performed at seven different submergence depths,ranging from D/LOA=0.0635 to D/LOA=0.635,and at two different speeds with Froude numbers of 0.21 and 0.33.The behaviors of the hydrodynamic forces and pitching moment for different operation depths were comprehensively analyzed.The results of the numerical analyses provide valuable insights into the hydrodynamic performance of semisubmersible naval ships,highlighting the critical factors influencing their resistance,powering,and maneuvering capabilities in both at-surface and submerged conditions.
文摘The main ideas in the development of the solvent extraction mixer settler focused on achieving clean phase separation,minimizing the loss of the reagents and decreasing the surface area of the settlers.The role of baffles in a mechanically agitated vessel is to ensure even distribution,reduce settler turbulence,promote the stability of power drawn by the impeller and to prevent swirling and vortexing of liquid,thus,greatly improving the mixing of liquid.The insertion of the appropriate number of baffles clearly improves the extent of liquid mixing.However,excessive baffling would interrupt liquid mixing and lengthen the mixing time.Computational fluid dynamics(CFD) provides a tool for determining detailed information on fluid flow(hydrodynamics) which is necessary for modeling subprocesses in mixer settler.A total of 54 final CFD runs were carried out representing different combinations of variables like number of baffles,density and impeller speed.CFD data shows that amount of separation increases with increasing baffles number and decreasing impeller speed.
文摘This paper presents a time-efficient numerical approach to modelling high explosive(HE)blastwave propagation using Computational Fluid Dynamics(CFD).One of the main issues of using conventional CFD modelling in high explosive simulations is the ability to accurately define the initial blastwave properties that arise from the ignition and consequent explosion.Specialised codes often employ Jones-Wilkins-Lee(JWL)or similar equation of state(EOS)to simulate blasts.However,most available CFD codes are limited in terms of EOS modelling.They are restrictive to the Ideal Gas Law(IGL)for compressible flows,which is generally unsuitable for blast simulations.To this end,this paper presents a numerical approach to simulate blastwave propagation for any generic CFD code using the IGL EOS.A new method known as the Input Cavity Method(ICM)is defined where input conditions of the high explosives are given in the form of pressure,velocity and temperature time-history curves.These time history curves are input at a certain distance from the centre of the charge.It is shown that the ICM numerical method can accurately predict over-pressure and impulse time history at measured locations for the incident,reflective and complex multiple reflection scenarios with high numerical accuracy compared to experimental measurements.The ICM is compared to the Pressure Bubble Method(PBM),a common approach to replicating initial conditions for a high explosive in Finite Volume modelling.It is shown that the ICM outperforms the PBM on multiple fronts,such as peak values and overall overpressure curve shape.Finally,the paper also presents the importance of choosing an appropriate solver between the Pressure Based Solver(PBS)and Density-Based Solver(DBS)and provides the advantages and disadvantages of either choice.In general,it is shown that the PBS can resolve and capture the interactions of blastwaves to a higher degree of resolution than the DBS.This is achieved at a much higher computational cost,showing that the DBS is much preferred for quick turnarounds.
文摘Computational fluid dynamics （CFD） plays a major role in predicting the flow behavior of a ship. With the development of fast computers and robust CFD software, CFD has become an important tool for designers and engineers in the ship industry. In this paper, the hull form of a ship was optimized for total resistance using CFD as a calculation tool and a genetic algorithm as an optimization tool. CFD based optimization consists of major steps involving automatic generation of geometry based on design parameters, automatic generation of mesh, automatic analysis of fluid flow to calculate the required objective/cost function, and finally an optimization tool to evaluate the cost for optimization. In this paper, integration of a genetic algorithm program, written in MATLAB, was carried out with the geometry and meshing software GAMBIT and CFD analysis software FLUENT. Different geometries of additive bulbous bow were incorporated in the original hull based on design parameters. These design variables were optimized to achieve a minimum cost function of ＂total resistance＂. Integration of a genetic algorithm with CFD tools proves to be effective for hull form ootimization.
基金support by the National Basic Research Program (Grant No. 2010CB226906,and 2012CB215000)
文摘A three-dimensional model for gas-solid flow in a circulating fluidized bed（CFB） riser was developed based on computational particle fluid dynamics（CPFD）.The model was used to simulate the gas-solid flow behavior inside a circulating fluidized bed riser operating at various superficial gas velocities and solids mass fluxes in two fluidization regimes,a dilute phase transport（DPT） regime and a fast fluidization（FF） regime.The simulation results were evaluated based on comparison with experimental data of solids velocity and holdup,obtained from non-invasive automated radioactive particle tracking and gamma-ray tomography techniques,respectively.The agreement of the predicted solids velocity and holdup with experimental data validated the CPFD model for the CFB riser.The model predicted the main features of the gas-solid flows in the two regimes;the uniform dilute phase in the DPT regime,and the coexistence of the dilute phase in the upper region and the dense phase in the lower region in the FF regime.The clustering and solids back mixing in the FF regime were stronger than those in the DPT regime.
基金Funded by National Science Foundation(No.50778415 and No.50878177)
文摘We investigated the effect of supply air rate and temperature on formaldehyde emission characteristics in an environment chamber.A three-dimensional computational fluid dynamics(CFD) chamber model for simulating formaldehyde emission in twelve different cases was developed for obtaining formaldehyde concentration by the area-weighted average method.Laboratory experiments were conducted in an environment chamber to validate the simulation results of twelve different cases and the formaldehyde concentration was measured by continuous sampling.The results show that there was good agreement between the model prediction and the experimental values within 4.3 difference for each case.The CFD simulation results varied in the range from 0.21 mg/m3 to 0.94 mg/m3,and the measuring results in the range from 0.17 mg/m3 to 0.87 mg/m3.The variation trend of formaldehyde concentration with supply air rate and temperature variation for CFD simulation and experiment measuring was consistent.With the existence of steady formaldehyde emission sources,formaldehyde concentration generally increased with the increase of temperature,and it decreased with the increase of air supply rate.We also provided some reasonable suggestions to reduce formaldehyde concentration and to improve indoor air quality for newly decorated rooms.
基金sponsored by the Alpha Foundation for the Improvement of Mine Safety and Health, Inc. (Alpha Foundation)
文摘This work proposes a vibrating mesh screen as an alternative to the static mesh screen currently used in conventional flooded-bed dust scrubbers for removing airborne coal mine dust in the continuous mining environment.Fundamental assessments suggest that a vibrating screen may improve the dust collection efficiency of scrubber systems and mitigate the clogging issues associated with the conventional design.To evaluate this hypothesis,computational fluid dynamics(CFD)simulations were carried out to assess the effects of vibration conditions(i.e.,frequency and amplitude)on the dust particle-mesh interaction and mesh wetting conditions,which are the two decisive factors in determining the dust collection efficiency.The results suggest that the vibrating mesh screen can enhance dust particle collision opportunities on the mesh and increase mesh wetted area as compared to the static mesh screen.The effects of mesh screen aperture,coal dust concentration,and spray nozzle flow rate on the performance of the vibrating mesh are also evaluated.Finally,a simplified three-phase flow simulation including airflow,dust particles,and water droplet spray is performed,and the results reflect a significant improvement of dust collection efficiency in the liquid-coated vibrating mesh screen.
文摘The computational fluid dynamics(CFD) code, FLUENT, was used to simulate the liquid-phase FCC diesel hydrotreating tubular reactor with a ceramic membrane tube dispenser. The chemical reaction and reaction heat were added to the model by user-defined function(UDF), showing the distribution of temperature and content of sulfides, nitrides, bicyclic aromatics and monocyclic aromatics in different parts of the reaction bed. When the pressure was 6.5 MPa, the amount of mixing hydrogen was 0.84%(m), the space velocity was 2 h-1 and the inlet temperature was 633 K, the temperature reached a maximum at a height of 0.15 m, and the range of radial temperature reached its maximum(2.5 K) at a height of 0.15 m. It indicated that the proper ratio of height to diameter of catalyst bed in the tubular reactor was 5-6. The increase of inlet temperature, the mixing hydrogen and the decrease of space velocity led to the decrease in the content of bicyclic aromatics, sulfides and nitrides, and the increase in monocyclic aromatics content, while the high temperature increased. The results were in good agreement with experimental data, indicating to the high accuracy of the model.
基金The authors acknowledge all the members of the Swissloop Team for their great endeavor to compete in the Hyperloop pod Competition and to push the Hyperloop technology forward.The authors gratefully acknowledge Connova AG for their support in manufacturing of the pod.
文摘Three-dimensional compressible flow simulationswere conducted to develop a Hyperloop pod. Thenovelty is the usage of Gamma transition model, in whichthe transition from laminar to turbulent flow can be predicted.First, a mesh dependency study was undertaken,showing second-order convergence with respect to themesh refinement. Second, an aerodynamic analysis for twodesigns, short and optimized, was conducted with thetraveling speed 125 m/s at the system pressure 0.15 bar.The concept of the short model was to delay the transitionto decrease the frictional drag;meanwhile that of theoptimized design was to minimize the pressure drag bydecreasing the frontal area and introduce the transitionmore toward the front of the pod. The computed resultsshow that the transition of the short model occurred moreon the rear side due to the pod shape, which resulted in 8%smaller frictional drag coefficient than that for the optimizedmodel. The pressure drag for the optimized designwas 24% smaller than that for the short design, half ofwhich is due to the decrease in the frontal area, and theother half is due to the smoothed rear-end shape. The totaldrag for the optimized model was 14% smaller than that forthe short model. Finally, the influence of the systempressure was investigated. As the system pressure and theReynolds number increase, the frictional drag coefficientincreases, and the transition point moves toward the front,which are the typical phenomena observed in the transitionregime.
基金Supported by the National Key R&D Program of China under Grant No 2016YFB0400104
文摘Metal organic chenlical vapor deposition （AIOCVD） growth systems arc one of the. main types of equipment used for growing single crystal materials, such as GaN. To obtain fihn epitaxial materials with uniform performanee, the flow field and ternperature field in a GaN-MOCVD reactor are investigated by modeling and simulating. To make the simulation results more consistent with the actual situation, the gases in the reactor are considered to be compressible, making it possible to investigate the distributions of gas density and pressure in the reactor. The computational fluid dynamics method is used to stud,v the effects of inlet gas flow velocity, pressure in the reactor, rotational speed of graphite susceptor, and gases used in the growth, which has great guiding~ significance for the growth of GaN fihn materials.
文摘Left ventricular assist device( LVAD) in this study is a mechanical tool that is used to support blood flow in the patient with heart disease. It supports left ventricle by building up the pressure to the pump outlet connected to the aorta. This pump was designed based on the magnetic driven centrifugal pump with a unique small washout hole constructed inside the impeller to generate the washout flow passage to prevent the stagnation at the region underneath and around the rotor. Computational fluid dynamics( CFD) was adopted in this study to assess the performance and optimize the design to avoid recirculation and high shear stress which is the main cause of stagnation and blood damage. Transient simulation was used for this study due to the asymmetric design of the washout hole and the complication of the bottom support of the impeller that has a risk of thrombosis,also,it was used to predict the variation of hydraulic performance caused by the rotation of the impeller and pulsed flow at the pump inlet. The simulation results show no excessive stress and no recirculation observed within the computational domain; in addition,the research result also provides information for further optimization and development to the pump.
基金sponsored by Bureau Veritas under the administration of Dr.ime Malenica
文摘In Fluid Structure Interaction(FSI) problems encountered in marine hydrodynamics, the pressure field and the velocity of the rigid body are tightly coupled. This coupling is traditionally resolved in a partitioned manner by solving the rigid body motion equations once per nonlinear correction loop, updating the position of the body and solving the fluid flow equations in the new configuration. The partitioned approach requires a large number of nonlinear iteration loops per time–step. In order to enhance the coupling, a monolithic approach is proposed in Finite Volume(FV) framework,where the pressure equation and the rigid body motion equations are solved in a single linear system. The coupling is resolved by solving the rigid body motion equations once per linear solver iteration of the pressure equation, where updated pressure field is used to calculate new forces acting on the body, and by introducing the updated rigid body boundary velocity in to the pressure equation. In this paper the monolithic coupling is validated on a simple 2D heave decay case. Additionally, the method is compared to the traditional partitioned approach(i.e. "strongly coupled" approach) in terms of computational efficiency and accuracy. The comparison is performed on a seakeeping case in regular head waves, and it shows that the monolithic approach achieves similar accuracy with fewer nonlinear correctors per time–step. Hence, significant savings in computational time can be achieved while retaining the same level of accuracy.
基金the project PTDC/EMSTRA/5628/2014 "Maneuvering and moored ships in ports-physical and numerical modeling,"funded by the Portuguese Foundation for Science and Technology(FCT)financed by FCT under contract number SFRH/BD/67070/2009
文摘A numerical study of ship-to-ship interaction forces is performed using a commercial CFD code,and the results are compared with experimental data and with the results of a panel method analysis.Two ship models have been used in the interaction forces analysis:a tug and a tanker,advancing parallel to each other with different lateral distances and two different values of the fluid depth.Computations are carried out with four different flow models:inviscid and viscous flow with the free surface modeled as a rigid wall and inviscid and viscous flow with the deformable free surface.A fair agreement was obtained with available experimental data and results obtained by panel method.The influence of viscosity in the computations is found to be comparatively weak,while the wavemaking effects may be important,at small magnitude of the horizontal clearance.
文摘In the present paper,the hydrodynamic performance of stepped planing craft is investigated by computational fluid dynamics(CFD)analysis.For this purpose,the hydrodynamic resistances of without step,one-step,and two-step hulls of Cougar planing craft are evaluated under different distances of the second step and LCG from aft,weight loadings,and Froude numbers(Fr).Our CFD results are appropriately validated against our conducted experimental test in National Iranians Marine Laboratory(NIMALA),Tehran,Iran.Then,the hydrodynamic resistance of intended planing crafts under various geometrical and physical conditions is predicted using artificial neural networks(ANNs).CFD analysis shows two different trends in the growth rate of resistance to weight ratio.So that,using steps for planing craft increases the resistance to weight ratio at lower Fr and decreases it at higher Fr.Additionally,by the increase of the distance between two steps,the resistance to weight ratio is decreased and the porpoising phenomenon is delayed.Furthermore,we obtained the maximum mean square error of ANNs output in the prediction of resistance to weight ratio equal to 0.0027.Finally,the predictive equation is suggested for the resistance to weight ratio of stepped planing craft according to weights and bias of designed ANNs.
基金support of RSSB to this work via the project RSSB/COF-UOH-49 is greatly appreciated.The authors also acknowledge the support by FCT,through IDMEC,under LAETA,project UIDB/50022/2020.
文摘Appropriate interaction between pantograph and catenary is imperative for smooth operation of electric trains.Changing heights of overhead lines to accommodate level crossings,overbridges,and tunnels pose significant challenges in maintaining consistent current collection performance as the pantograph aerodynamic profile,and thus aerodynamic load changes significantly with operational height.This research aims to analyse the global flow characteristics and aerodynamic forces acting on individual components of an HSX pantograph operating in different configurations and orientations,such that the results can be combined with multibody simulations to obtain accurate dynamic insight into contact forces.Specifically,computational fluid dynamics simulations are used to investigate the pantograph component loads in a representative setting,such as that of the recessed cavity on a Class 800 train.From an aerodynamic perspective,this study indicates that the total drag force acting on non-fixed components of the pantograph is larger for the knuckle-leading orientation rather than the knuckle-trailing,although the difference between the two is found to reduce with increasing pantograph extension.Combining the aerodynamic loads acting on individual components with multibody tools allows for realistic dynamic insight into the pantograph behaviour.The results obtained show how considering aerodynamic forces enhance the realism of the models,leading to behaviour of the pantograph-catenary contact forces closely matching that seen in experimental tests.
基金supported by the National Basic Research Program of China(″973″Program)(No.2014CB046200)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20120073120014)
文摘To simulate floating offshore wind turbine(FOWT)in coupled wind-wave domain via CFD method,the NREL 5MW wind turbine supported by the OC3-Hywind Spar platform is modeled in the STAR-CCM+ software.Based on the Reynolds-averaged Navier-Stokes(RANS)equations and re-normalisation group(RNG)k-εturbulence model,the rotor aerodynamic simulation for wind turbine is conducted.Numerical results agree well with the NREL data.Taking advantage with the volume of fluid(VOF)method and dynamic fluid body interaction(DFBI)technology,the dynamic responses of the floating system with mooring lines are simulated under the coupled wind-wave sea condition.The free-decay tests for rigid-body degrees of freedom(DOFs)in still water and hydrodynamic tests in a regular wave are performed to validate the numerical model by comparing its result with the results simulated by FAST.Finally,the simulations of the overall FOWT system in the coupled wind-wave flow field are carried out.The relationship between the power output and dynamic motion responses of the platform is investigated.The numerical results show that the dynamic response of wind turbine performance and platform motions all vary in the same frequency as the inlet wave.During platform motion,the power output of wind turbine is more sensitive than the thrust force.This study may provide some reference for further research in the coupled aero-hydro simulation of FOWT.
文摘[Introduction] Accurate calculation of the hydrodynamic coefficients for floating structures and the investigation of the flow field distribution around floating bodies on the marine free surface are essential for improving the engineering design and application of marine structures.[Method] This study utilized the computational fluid dynamics(CFD) approach and the Reynolds Averaged NavierStokes(RANS) method and considered the effects of viscosity and free surface interactions on the hydrodynamic behavior of floating structures.By employing the dynamic mesh technique,this study simulated the periodic movements of simplified three-dimensional(3D)shapes:spheres,cylinders,and cubes,which were representative of complex marine structures.The volume of fluid(VOF) method was leveraged to accurately track the nonlinear behavior of the free surface.In this analysis,the added mass and damping coefficients for the fundamental modes of motion(surge,heave,and roll) were calculated across a spectrum of frequencies,facilitating the fast determination of hydrodynamic forces and moments exerted on floating structures.[Result] The results of this study are not only consistent with the results of the 3D potential flow theory but also further reflect the role of viscosity.This method can be used for precise calculation of the hydrodynamic coefficients of floating structures and for describing the flow field of such structures in motion on a free surface.[Conclusion] The methodology presented goes beyond the traditional potential flow approach.
