This paper aims to investigate a dam break in a channel with a bend in the presence of several obstacles.To accurately determine the flood zones,it is necessary to take into account many factors such as terrain,reserv...This paper aims to investigate a dam break in a channel with a bend in the presence of several obstacles.To accurately determine the flood zones,it is necessary to take into account many factors such as terrain,reservoir volume.Numerical modeling was used to determine the flood zone.Numerical modeling based on the Navier-Stokes equations with a turbulent k-epsilon RNG model,the Volume of Fluid(VOF)method and the PISO algorithm were used to analyze the flow in a bend channel at an angle of 10 with the obstacles.To verify the numerical model,a test on dam break in the 450 channel was conducted.The simulation results were compared with experimental data and with the numerical data of existing data.Having been convinced of the correctness of the mathematical model,the authors carried out a numerical simulation of the main problem in three versions:without barriers,with one obstacle,with two obstacles.According to the obtained numerical results,it can be noted that irregular landforms held the flow,a decrease in water level and a slower time for water emergence could be seen.Thus,the water flow without an obstacle,with one obstacle and with two obstacles showed 4.2 s,4.4 s and 4.6 s of the time of water appearance,respectively.This time shift can give a certain advantage when conducting various events to evacuate people.展开更多
To simulate two-dimensional free-surface flows with complex boundaries directly and accurately, a novel VOF (Volume-of-fluid) method based on unstructured quadrilateral mesh is presented. Without introducing any compl...To simulate two-dimensional free-surface flows with complex boundaries directly and accurately, a novel VOF (Volume-of-fluid) method based on unstructured quadrilateral mesh is presented. Without introducing any complicated boundary treatment or artificial diffusion, this method treated curved boundaries directly by utilizing the inherent merit of unstructured mesh in fitting curves. The PLIC (Piecewise Linear Interface Calculation) method was adopted to obtain a second-order accurate linearized reconstruction approximation and the MLER (Modified Lagrangian-Eulerian Re-map) method was introduced to advect fluid volumes on unstructured mesh. Moreover, an analytical relation for the interface’s line constant vs. the volume clipped by the interface was developed so as to improve the method’s efficiency. To validate this method, a comprehensive series of large straining advection tests were performed. Numerical results provide convincing evidences for the method’s high volume conservative accuracy and second-order shape error convergence rate. Also, a dramatic improvement on computational accuracy over its unstructured triangular mesh counterpart is checked.展开更多
The PLIC/SN method that combines the second-order volume tracking method (PLIC-VOF) with the equation of surface normal (SN) vector was recently proposed (M. Sun, “Volume Tracking of Subgrid Particles,” Internationa...The PLIC/SN method that combines the second-order volume tracking method (PLIC-VOF) with the equation of surface normal (SN) vector was recently proposed (M. Sun, “Volume Tracking of Subgrid Particles,” International Journal for Numerical Methods in Fluids, Vol. 66, No. 12, 2011, pp. 1530-1554). The method is able to track the motion of a subgrid particle, but the accuracy is not as good as expected on high resolution grids for vortical flows. In this paper, a simple unsplit multidimensional advection algorithm is coupled with the equation of SN vector. The advection algorithm is formulated as the finite volume method, so that it can be used readily for both structured and unstructured grids while maintaining the exact mass conservation. The new method improves the accuracy significantly for high resolution grids. In the well-known test of the time-resolved vortex problem of T = 2, the circular interface is resolved with an accuracy better than ever using the equation of SN vector.展开更多
A two-dimensional numerical model based on the Navier-Stokes equations and computational Lagrangian-Eulerian advection remap-volume of fluid （CLEAR-VOF） method was developed to simulate wave and flow problems. The N...A two-dimensional numerical model based on the Navier-Stokes equations and computational Lagrangian-Eulerian advection remap-volume of fluid （CLEAR-VOF） method was developed to simulate wave and flow problems. The Navier-Stokes equations were discretized with a three-step finite element method that has a third-order accuracy. In the CLEAR-VOF method, the VOF function F was calculated in the Lagrangian manner and allowed the complicated free surface to be accurately captured. The propagation of regular waves and solitary waves over a flat bottom, and shoaling and breaking of solitary waves on two different slopes were simulated with this model, and the numerical results agreed with experimental data and theoretical solutions. A benchmark test of dam-collapse flow was also simulated with an unstructured mesh, and the capability of the present model for wave and flow simulations with unstructured meshes, was verified. The results show that the model is effective for numerical simulation of wave and flow problems with both structured and unstructured meshes.展开更多
VOF(Volume Of Fluid)方法能够通过在欧拉网格上使用离散的体积分数域表示光滑界面,在不可混合流体的数值模拟中得到广泛应用。针对多相流仿真中的液滴曲率计算问题,开发了一种计算界面曲率的算法。首先提出了一种新的数据生成方法,在...VOF(Volume Of Fluid)方法能够通过在欧拉网格上使用离散的体积分数域表示光滑界面,在不可混合流体的数值模拟中得到广泛应用。针对多相流仿真中的液滴曲率计算问题,开发了一种计算界面曲率的算法。首先提出了一种新的数据生成方法,在液滴界面上进行随机采样,增强网格内体积分数的信息量,并调整取值范围以覆盖正负曲率。然后改进了传统的深度神经网络(DNN)模型,使其在计算曲率时保持对称性。基于VOF方法与该模型,利用目标单元及邻近单元体积分数计算曲率。最后选取最优模型并应用于Basilisk软件中,以提高计算曲率的准确性和稳定性。测试结果表明,其计算曲率时准确稳定。在计算小半径液滴曲率时,误差减小了25%至50%,并能用于液滴融合仿真,证明了其应用价值。展开更多
本文研究的目的在于,使用分段线性PLIC(Piecewise Linear Interface Construction)方式构造界面,推导三维空间中的VOF(Volume of Fluid)算法PLIC3D,给出详尽的计算公式和过程。然后,用球形流体匀速运动作为分析PLIC3D算法的数值算例,比...本文研究的目的在于,使用分段线性PLIC(Piecewise Linear Interface Construction)方式构造界面,推导三维空间中的VOF(Volume of Fluid)算法PLIC3D,给出详尽的计算公式和过程。然后,用球形流体匀速运动作为分析PLIC3D算法的数值算例,比较了PLIC3D和分段常数PCIC(Piecewise Constant Interface Construction)构造法中DA3D(Donor-Acceptor in 3-Dimension)在三维空间计算界面的差别。结果显示PLIC3D优于DA3D,它能够更好地保持流体在平移运动中的形状,证实了PLIC方式的空间构造精度高于PCIC的结论。最后,利用PLIC3D计算自由面,模拟容器中流体泄漏问题,得到了其液面形状变化和速度场。展开更多
Investigating the wave field near structures in coastal and offshore engineering is of increasing significance. In the present study, simulation is done of the wave profile and flow field for waves propagating over su...Investigating the wave field near structures in coastal and offshore engineering is of increasing significance. In the present study, simulation is done of the wave profile and flow field for waves propagating over submerged bars, using PLIC-VOF （Pieeewise Linear Interface Construction） to trace the free surface of wave and finite difference method to solve vertical 2D Navier-Stokes （N-S） equations. A comparison of the numerical results for two kinds of submerged bars with the experimental ones shows that the PLIC-VOF model used in this study is effective and can compute the wave field precisely.展开更多
A vertical two-dimensional numerical model has been applied to solving the Reynolds Averaged Navier- Stokes （RANS} equations in the simulation of current and wave propagation through vegetated and non- vegetated wate...A vertical two-dimensional numerical model has been applied to solving the Reynolds Averaged Navier- Stokes （RANS} equations in the simulation of current and wave propagation through vegetated and non- vegetated waters. The k-e model is used for turbulence closure of RANS equations. The effect of vegeta- tion is simulated by adding the drag force of vegetation in the flow momentum equations and turbulence model. To solve the modified N-S equations, the finite difference method is used with the staggered grid system to solver equations. The Youngs＇ fractional volume of fluid （VOF） is applied tracking the free sur- face with second-order accuracy. The model has been tested by simulating dam break wave, pure current with vegetation, solitary wave runup on vegetated and non-vegetated channel, regular and random waves over a vegetated field. The model reasonably well reproduces these experimental observations, the model- ing approach presented herein should be useful in simulating nearshore processes in coastal domains with vegetation effects.展开更多
A numerical irregular wave flume with active absorption of re-reflected waves is simulated by use of volume of fluid （VOF） method. An active ＇absorbing wave-maker based on linear wave theory is set on the left boun...A numerical irregular wave flume with active absorption of re-reflected waves is simulated by use of volume of fluid （VOF） method. An active ＇absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume. The progressive waves and the absorbing waves are generated simultaneously at the active wave generating-absorbing boundary. The absorbing waves are generated to eliminate the waves coming back to the generating boundary due to reflection from the outflow boundary and the structures. SIRW method proposed by Frigaard and Brorsen （1995） is used to separate the incident waves and reflected waves. The digital filters are designed based on the surface elevation signals of the two wave gauges. The corrected velocity of the wave-maker paddle is the output from the digital filter in real time. The numerical results of regular and irregular waves by the active absorbing-generating boundary are compared with the numerical results by the ordinary generating boundary to verify the performance of the active absorbing-generator boundary. The differences between the initial incident waves and the estimated incident waves are analyzed.展开更多
VOF(Volume of Fluid)方法由于其良好的守恒性和网格适应性,且具有计算资源需求相对较小等优点,成为船舶水动力学领域自由面流动CFD(Computational Fluid Dynamics)模拟的主流方法。但原始的VOF方法存在较为严重的界面扩散问题,导致模...VOF(Volume of Fluid)方法由于其良好的守恒性和网格适应性,且具有计算资源需求相对较小等优点,成为船舶水动力学领域自由面流动CFD(Computational Fluid Dynamics)模拟的主流方法。但原始的VOF方法存在较为严重的界面扩散问题,导致模拟的界面厚度过大、空间分辨率不够,进而影响流场相关变量的计算精度,这一问题在非定常自由面流动模拟中尤为明显。本文针对上述问题,通过在VOF控制方程中引入人工对流项以达到抑制界面扩散、压缩界面厚度的目的,并采用隐式离散人工对流项的方式提高计算稳定性,形成了反扩散VOF算法。经Zalesak和剪切场等经典算例在不同数量网格下的测试验证,表明反扩散VOF算法能够大幅压缩界面厚度,同时明显减小质量误差。随后的三维无障碍溃坝算例和破舱进水算例,进一步证明了反扩散VOF算法在实际非定常流动模拟中能够更好地捕捉自由面并提高计算精度。展开更多
This is a numerical study of a falling droplet surrounding by air under the electric field modeled with finite volume method by means of CFD.The VOF method has been employed to model the two-phase flow of the present ...This is a numerical study of a falling droplet surrounding by air under the electric field modeled with finite volume method by means of CFD.The VOF method has been employed to model the two-phase flow of the present study.Various capillary numbers are investigated to analyze the effects of electric field intensity on the falling droplet deformation.Also,the effects of electric potential on the heat transfer coefficient have been examined.The obtained results showed that by applying the electric field at a capillary number of 0.2 the droplet tends to retain its primitive shape as time goes by,with a subtle deformation to an oblate form.Intensifying the electric field to a capillary number of 0.8 droplet deformation is almost insignificantwith time progressing;however,further enhancement in capillary number to 2 causes the droplet to deform as a prolate shape and higher values of this number intensify the prolate form deformation of the droplet and result in pinch-off phenomenon.Ultimately,it is showed that as the electric potential augments the heat transfer coefficient increases in which for electric potential values higher than 2400 V the heat transfer coefficient enhances significantly.展开更多
A stencil-like volume of fluid （VOF） method is proposed for tracking free interface. A stencil on a grid cell is worked out according to the normal direction of the interface, in which only three interface positions...A stencil-like volume of fluid （VOF） method is proposed for tracking free interface. A stencil on a grid cell is worked out according to the normal direction of the interface, in which only three interface positions are possible in 2D cases, and the interface can be reconstructed by only requiring the known local volume fraction information. On the other hand, the fluid-occupying-length is defined on each side of the stencil, through which a unified fluid-occupying volume model and a unified algorithm can be obtained to solve the interface advection equation. The method is suitable for the arbitrary geometry of the grid cell, and is extendible to 3D cases. Typical numerical examples show that the current method can give ＂sharp＂ results for tracking free interface.展开更多
Sediments in the seabed hold vital clues to the study of marine geology,microbial communities and history of ocean life,and the remote operated vehicle(ROV)mounted tubular sampling is an important way to obtain sedime...Sediments in the seabed hold vital clues to the study of marine geology,microbial communities and history of ocean life,and the remote operated vehicle(ROV)mounted tubular sampling is an important way to obtain sediments.However,sampling in the seabed is a particularly difficult and complicated task due to the difficulty accessing deep water layers.The sampling is affected by the sampler’s structural parameters,operation parameters and the interaction between the sampling tube and sediments,which usually results in low volume and coring rate of sediments obtained.This paper simulated the soft viscous seabed sediments as non-Newtonian Herschel-Bulkley viscoplastic fluids and established a numerical model for the tubular sampling based on the volume of fluid(VOF)method.The influence rules of the sampling tube diameter,drainage area rate,penetration velocity,and sediments dynamic viscosity on coring rate and volume were studied.The results showed that coring volume was negatively correlated with all the parameters except the sampling tube diameter.Furthermore,coring rate decreased with increases in penetration velocity,drainage area rate,and sediments dynamic viscosity.The coring rate first increased and then decreased with increasing of the sampling tube diameter,and the peak value was also influenced by penetration velocity.Then,based on the numerical simulation results,an experimental sampling platform was set up and real-world sampling experiments were conducted.The simulation results tallied with the experimental results,with a maximum absolute error of only 4.6%,which verified that the numerical simulation model accurately reflected real-world sampling.The findings in this paper can provide a theoretical basis for facilitating the optimal design of the geometric structure of the seabed sediments samplers and the parameters in the sampling process.展开更多
Jetting succeeded by accumulation is the characteristic of the vacuum filling,which is different from the conventional pressure-driven flow.In order to simulate this kind of flow,a three-dimensional theoretical model ...Jetting succeeded by accumulation is the characteristic of the vacuum filling,which is different from the conventional pressure-driven flow.In order to simulate this kind of flow,a three-dimensional theoretical model in terms of incompressible and viscous flow is established,and an iterative method combined with finite element method(FEM)is proposed to solve the flow problem.The Lagranian-VOF method is constructed to trace the jetting and accumulated flow fronts.Based on the proposed model and algorithm,a simulation program is developed to predict the velocity,pressure,temperature,and advancement progress.To validate the model and algorithm,a visual experimental equipment for vacuum filling is designed and construted.The vacuum filling experiments with different viscous materials and negative pressures were conducted and compared with the corresponding simulations.The results show the flow front shape closely depends on the fluid viscosity and less relates to the vacuum pressure.展开更多
CO_(2)capture and storage technology is favorable for the reduction of CO_(2)emissions.In recent years,a great number of research achievements have been obtained on CO_(2)geological storage from nano scale to oil/gas ...CO_(2)capture and storage technology is favorable for the reduction of CO_(2)emissions.In recent years,a great number of research achievements have been obtained on CO_(2)geological storage from nano scale to oil/gas reservoir scale,but most studies only focus on theflow behaviors in single-dimension porous media.Besides,the physical experiment method is influenced by many uncertain factors and consumes a lot of time and cost.In order to deeply understand theflow behaviors in the process of CO_(2)geological storage in microscopic view and increase the volume of CO_(2)geological storage,this paper established 2D and 3D models by using VOF(Volume of Fluid)method which can track the dynamic change of two-phase interface,to numerically simulate supercritical CO_(2)-brine two-phaseflow.Then,the distribution characteristics of CO_(2)clusters and the variation laws of CO_(2)saturation under different wettability,capillary number and viscosity ratio conditions were compared,and the intrinsic mechanisms of CO_(2)storage at pore scale were revealed.And the following research results were obtained.First,with the increase of rock wettability to CO_(2),the sweep range of CO_(2)enlarged,and the disconnection frequency of CO_(2)clusters deceased,and thus the volume of CO_(2)storage increased.Second,with the increase of capillary number,the displacement mode transformed from capillaryfingering to stable displacement,and thus the volume of CO_(2)storage increased.Third,as the viscosity of injected supercritical CO_(2)gradually approached that of brine,theflow resistance between two-phasefluids decreased,promoting the"lubricating effect".As a result,theflow capacity of CO_(2)phase was improved,and thus the volume of CO_(2)storage was increased.Fourth,the influence degrees of wettability,capillary number and viscosity ratio on CO_(2)saturation were different in multi-dimensional porous media models.In conclusion,the CO_(2)-brine two-phaseflow simulation based on VOF method revealed theflow mechanisms in the process of CO_(2)geological storage at pore scale,which is of guiding significance to the development of CCUS technology and provides theoretical guidance and technical support for the study of CO_(2)geological storage in a larger scale.展开更多
基金supported by the grant from the Ministry of science and Higher education of the Republic of Kazakhstan(AP23489948).
文摘This paper aims to investigate a dam break in a channel with a bend in the presence of several obstacles.To accurately determine the flood zones,it is necessary to take into account many factors such as terrain,reservoir volume.Numerical modeling was used to determine the flood zone.Numerical modeling based on the Navier-Stokes equations with a turbulent k-epsilon RNG model,the Volume of Fluid(VOF)method and the PISO algorithm were used to analyze the flow in a bend channel at an angle of 10 with the obstacles.To verify the numerical model,a test on dam break in the 450 channel was conducted.The simulation results were compared with experimental data and with the numerical data of existing data.Having been convinced of the correctness of the mathematical model,the authors carried out a numerical simulation of the main problem in three versions:without barriers,with one obstacle,with two obstacles.According to the obtained numerical results,it can be noted that irregular landforms held the flow,a decrease in water level and a slower time for water emergence could be seen.Thus,the water flow without an obstacle,with one obstacle and with two obstacles showed 4.2 s,4.4 s and 4.6 s of the time of water appearance,respectively.This time shift can give a certain advantage when conducting various events to evacuate people.
基金the National Natural Science Foundation ofChina under Grant No. 50779043, 50779045
文摘To simulate two-dimensional free-surface flows with complex boundaries directly and accurately, a novel VOF (Volume-of-fluid) method based on unstructured quadrilateral mesh is presented. Without introducing any complicated boundary treatment or artificial diffusion, this method treated curved boundaries directly by utilizing the inherent merit of unstructured mesh in fitting curves. The PLIC (Piecewise Linear Interface Calculation) method was adopted to obtain a second-order accurate linearized reconstruction approximation and the MLER (Modified Lagrangian-Eulerian Re-map) method was introduced to advect fluid volumes on unstructured mesh. Moreover, an analytical relation for the interface’s line constant vs. the volume clipped by the interface was developed so as to improve the method’s efficiency. To validate this method, a comprehensive series of large straining advection tests were performed. Numerical results provide convincing evidences for the method’s high volume conservative accuracy and second-order shape error convergence rate. Also, a dramatic improvement on computational accuracy over its unstructured triangular mesh counterpart is checked.
文摘The PLIC/SN method that combines the second-order volume tracking method (PLIC-VOF) with the equation of surface normal (SN) vector was recently proposed (M. Sun, “Volume Tracking of Subgrid Particles,” International Journal for Numerical Methods in Fluids, Vol. 66, No. 12, 2011, pp. 1530-1554). The method is able to track the motion of a subgrid particle, but the accuracy is not as good as expected on high resolution grids for vortical flows. In this paper, a simple unsplit multidimensional advection algorithm is coupled with the equation of SN vector. The advection algorithm is formulated as the finite volume method, so that it can be used readily for both structured and unstructured grids while maintaining the exact mass conservation. The new method improves the accuracy significantly for high resolution grids. In the well-known test of the time-resolved vortex problem of T = 2, the circular interface is resolved with an accuracy better than ever using the equation of SN vector.
基金supported by the National Natural Science Foundation of China (Grant No. 50679008)
文摘A two-dimensional numerical model based on the Navier-Stokes equations and computational Lagrangian-Eulerian advection remap-volume of fluid （CLEAR-VOF） method was developed to simulate wave and flow problems. The Navier-Stokes equations were discretized with a three-step finite element method that has a third-order accuracy. In the CLEAR-VOF method, the VOF function F was calculated in the Lagrangian manner and allowed the complicated free surface to be accurately captured. The propagation of regular waves and solitary waves over a flat bottom, and shoaling and breaking of solitary waves on two different slopes were simulated with this model, and the numerical results agreed with experimental data and theoretical solutions. A benchmark test of dam-collapse flow was also simulated with an unstructured mesh, and the capability of the present model for wave and flow simulations with unstructured meshes, was verified. The results show that the model is effective for numerical simulation of wave and flow problems with both structured and unstructured meshes.
文摘VOF(Volume Of Fluid)方法能够通过在欧拉网格上使用离散的体积分数域表示光滑界面,在不可混合流体的数值模拟中得到广泛应用。针对多相流仿真中的液滴曲率计算问题,开发了一种计算界面曲率的算法。首先提出了一种新的数据生成方法,在液滴界面上进行随机采样,增强网格内体积分数的信息量,并调整取值范围以覆盖正负曲率。然后改进了传统的深度神经网络(DNN)模型,使其在计算曲率时保持对称性。基于VOF方法与该模型,利用目标单元及邻近单元体积分数计算曲率。最后选取最优模型并应用于Basilisk软件中,以提高计算曲率的准确性和稳定性。测试结果表明,其计算曲率时准确稳定。在计算小半径液滴曲率时,误差减小了25%至50%,并能用于液滴融合仿真,证明了其应用价值。
文摘本文研究的目的在于,使用分段线性PLIC(Piecewise Linear Interface Construction)方式构造界面,推导三维空间中的VOF(Volume of Fluid)算法PLIC3D,给出详尽的计算公式和过程。然后,用球形流体匀速运动作为分析PLIC3D算法的数值算例,比较了PLIC3D和分段常数PCIC(Piecewise Constant Interface Construction)构造法中DA3D(Donor-Acceptor in 3-Dimension)在三维空间计算界面的差别。结果显示PLIC3D优于DA3D,它能够更好地保持流体在平移运动中的形状,证实了PLIC方式的空间构造精度高于PCIC的结论。最后,利用PLIC3D计算自由面,模拟容器中流体泄漏问题,得到了其液面形状变化和速度场。
文摘Investigating the wave field near structures in coastal and offshore engineering is of increasing significance. In the present study, simulation is done of the wave profile and flow field for waves propagating over submerged bars, using PLIC-VOF （Pieeewise Linear Interface Construction） to trace the free surface of wave and finite difference method to solve vertical 2D Navier-Stokes （N-S） equations. A comparison of the numerical results for two kinds of submerged bars with the experimental ones shows that the PLIC-VOF model used in this study is effective and can compute the wave field precisely.
基金The National Natural Science Foundation of China under contract No.51279023the Public Science and Technology Research Funds Projects of Ocean under contract No.201205023+1 种基金the Special Funds for Postdoctoral Innovative Projects of Liaoning Province of China under contract No.2011921018the Special Funds for Talent Projects of Dalian Ocean University under contract No.SYYJ2011004
文摘A vertical two-dimensional numerical model has been applied to solving the Reynolds Averaged Navier- Stokes （RANS} equations in the simulation of current and wave propagation through vegetated and non- vegetated waters. The k-e model is used for turbulence closure of RANS equations. The effect of vegeta- tion is simulated by adding the drag force of vegetation in the flow momentum equations and turbulence model. To solve the modified N-S equations, the finite difference method is used with the staggered grid system to solver equations. The Youngs＇ fractional volume of fluid （VOF） is applied tracking the free sur- face with second-order accuracy. The model has been tested by simulating dam break wave, pure current with vegetation, solitary wave runup on vegetated and non-vegetated channel, regular and random waves over a vegetated field. The model reasonably well reproduces these experimental observations, the model- ing approach presented herein should be useful in simulating nearshore processes in coastal domains with vegetation effects.
基金supported by the‘New Century Outstanding Talent’Scheme of the Ministry of Education of China(Grant No.NCET-07-0135)
文摘A numerical irregular wave flume with active absorption of re-reflected waves is simulated by use of volume of fluid （VOF） method. An active ＇absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume. The progressive waves and the absorbing waves are generated simultaneously at the active wave generating-absorbing boundary. The absorbing waves are generated to eliminate the waves coming back to the generating boundary due to reflection from the outflow boundary and the structures. SIRW method proposed by Frigaard and Brorsen （1995） is used to separate the incident waves and reflected waves. The digital filters are designed based on the surface elevation signals of the two wave gauges. The corrected velocity of the wave-maker paddle is the output from the digital filter in real time. The numerical results of regular and irregular waves by the active absorbing-generating boundary are compared with the numerical results by the ordinary generating boundary to verify the performance of the active absorbing-generator boundary. The differences between the initial incident waves and the estimated incident waves are analyzed.
文摘VOF(Volume of Fluid)方法由于其良好的守恒性和网格适应性,且具有计算资源需求相对较小等优点,成为船舶水动力学领域自由面流动CFD(Computational Fluid Dynamics)模拟的主流方法。但原始的VOF方法存在较为严重的界面扩散问题,导致模拟的界面厚度过大、空间分辨率不够,进而影响流场相关变量的计算精度,这一问题在非定常自由面流动模拟中尤为明显。本文针对上述问题,通过在VOF控制方程中引入人工对流项以达到抑制界面扩散、压缩界面厚度的目的,并采用隐式离散人工对流项的方式提高计算稳定性,形成了反扩散VOF算法。经Zalesak和剪切场等经典算例在不同数量网格下的测试验证,表明反扩散VOF算法能够大幅压缩界面厚度,同时明显减小质量误差。随后的三维无障碍溃坝算例和破舱进水算例,进一步证明了反扩散VOF算法在实际非定常流动模拟中能够更好地捕捉自由面并提高计算精度。
文摘This is a numerical study of a falling droplet surrounding by air under the electric field modeled with finite volume method by means of CFD.The VOF method has been employed to model the two-phase flow of the present study.Various capillary numbers are investigated to analyze the effects of electric field intensity on the falling droplet deformation.Also,the effects of electric potential on the heat transfer coefficient have been examined.The obtained results showed that by applying the electric field at a capillary number of 0.2 the droplet tends to retain its primitive shape as time goes by,with a subtle deformation to an oblate form.Intensifying the electric field to a capillary number of 0.8 droplet deformation is almost insignificantwith time progressing;however,further enhancement in capillary number to 2 causes the droplet to deform as a prolate shape and higher values of this number intensify the prolate form deformation of the droplet and result in pinch-off phenomenon.Ultimately,it is showed that as the electric potential augments the heat transfer coefficient increases in which for electric potential values higher than 2400 V the heat transfer coefficient enhances significantly.
基金Project supported by the National Natural Science Foundation of China (No.10672097)Shanghai Leading Academic Discipline Project (No.Y0103)
文摘A stencil-like volume of fluid （VOF） method is proposed for tracking free interface. A stencil on a grid cell is worked out according to the normal direction of the interface, in which only three interface positions are possible in 2D cases, and the interface can be reconstructed by only requiring the known local volume fraction information. On the other hand, the fluid-occupying-length is defined on each side of the stencil, through which a unified fluid-occupying volume model and a unified algorithm can be obtained to solve the interface advection equation. The method is suitable for the arbitrary geometry of the grid cell, and is extendible to 3D cases. Typical numerical examples show that the current method can give ＂sharp＂ results for tracking free interface.
基金Supported by National Key R&D Program of China(Grant No.2016YFC0300502)the National Natural Science Foundation of China(Grant Nos.51705145 and 517779092)+1 种基金Scientific Research Fund of Hunan Provincial Education Department(Grant No.18B205)Hunan Province Natural Science Foundation(Grant No.2019 JJ50182).
文摘Sediments in the seabed hold vital clues to the study of marine geology,microbial communities and history of ocean life,and the remote operated vehicle(ROV)mounted tubular sampling is an important way to obtain sediments.However,sampling in the seabed is a particularly difficult and complicated task due to the difficulty accessing deep water layers.The sampling is affected by the sampler’s structural parameters,operation parameters and the interaction between the sampling tube and sediments,which usually results in low volume and coring rate of sediments obtained.This paper simulated the soft viscous seabed sediments as non-Newtonian Herschel-Bulkley viscoplastic fluids and established a numerical model for the tubular sampling based on the volume of fluid(VOF)method.The influence rules of the sampling tube diameter,drainage area rate,penetration velocity,and sediments dynamic viscosity on coring rate and volume were studied.The results showed that coring volume was negatively correlated with all the parameters except the sampling tube diameter.Furthermore,coring rate decreased with increases in penetration velocity,drainage area rate,and sediments dynamic viscosity.The coring rate first increased and then decreased with increasing of the sampling tube diameter,and the peak value was also influenced by penetration velocity.Then,based on the numerical simulation results,an experimental sampling platform was set up and real-world sampling experiments were conducted.The simulation results tallied with the experimental results,with a maximum absolute error of only 4.6%,which verified that the numerical simulation model accurately reflected real-world sampling.The findings in this paper can provide a theoretical basis for facilitating the optimal design of the geometric structure of the seabed sediments samplers and the parameters in the sampling process.
基金the National Science Foundation of China(No.11672271)Shenzhen Zhaowei Machinery&Electronics CO.,LTD.(No.20210035A and 20210035B)for this research work are gratefully acknowledged.
文摘Jetting succeeded by accumulation is the characteristic of the vacuum filling,which is different from the conventional pressure-driven flow.In order to simulate this kind of flow,a three-dimensional theoretical model in terms of incompressible and viscous flow is established,and an iterative method combined with finite element method(FEM)is proposed to solve the flow problem.The Lagranian-VOF method is constructed to trace the jetting and accumulated flow fronts.Based on the proposed model and algorithm,a simulation program is developed to predict the velocity,pressure,temperature,and advancement progress.To validate the model and algorithm,a visual experimental equipment for vacuum filling is designed and construted.The vacuum filling experiments with different viscous materials and negative pressures were conducted and compared with the corresponding simulations.The results show the flow front shape closely depends on the fluid viscosity and less relates to the vacuum pressure.
基金supported by the National Natural Science Foun-dation of China“Research on basic theory for development of deep and ultra-deep reservoirs”(No.52034010)“Flow control during drilling/production of ultra-deep oil and gas wells”(No.52288101).
文摘CO_(2)capture and storage technology is favorable for the reduction of CO_(2)emissions.In recent years,a great number of research achievements have been obtained on CO_(2)geological storage from nano scale to oil/gas reservoir scale,but most studies only focus on theflow behaviors in single-dimension porous media.Besides,the physical experiment method is influenced by many uncertain factors and consumes a lot of time and cost.In order to deeply understand theflow behaviors in the process of CO_(2)geological storage in microscopic view and increase the volume of CO_(2)geological storage,this paper established 2D and 3D models by using VOF(Volume of Fluid)method which can track the dynamic change of two-phase interface,to numerically simulate supercritical CO_(2)-brine two-phaseflow.Then,the distribution characteristics of CO_(2)clusters and the variation laws of CO_(2)saturation under different wettability,capillary number and viscosity ratio conditions were compared,and the intrinsic mechanisms of CO_(2)storage at pore scale were revealed.And the following research results were obtained.First,with the increase of rock wettability to CO_(2),the sweep range of CO_(2)enlarged,and the disconnection frequency of CO_(2)clusters deceased,and thus the volume of CO_(2)storage increased.Second,with the increase of capillary number,the displacement mode transformed from capillaryfingering to stable displacement,and thus the volume of CO_(2)storage increased.Third,as the viscosity of injected supercritical CO_(2)gradually approached that of brine,theflow resistance between two-phasefluids decreased,promoting the"lubricating effect".As a result,theflow capacity of CO_(2)phase was improved,and thus the volume of CO_(2)storage was increased.Fourth,the influence degrees of wettability,capillary number and viscosity ratio on CO_(2)saturation were different in multi-dimensional porous media models.In conclusion,the CO_(2)-brine two-phaseflow simulation based on VOF method revealed theflow mechanisms in the process of CO_(2)geological storage at pore scale,which is of guiding significance to the development of CCUS technology and provides theoretical guidance and technical support for the study of CO_(2)geological storage in a larger scale.
