In this work,a virtual body-fitted grid is introduced and combined with the implicit velocity correction-based immersed boundary method(IBM)for simulation of incompressible flows with moving boundaries.The original im...In this work,a virtual body-fitted grid is introduced and combined with the implicit velocity correction-based immersed boundary method(IBM)for simulation of incompressible flows with moving boundaries.The original implicit velocity correction-based IBM to this kind of problem requires the matrix inversion operation to be repeated at each time step,resulting in significant computational resources and time when the Gaussian elimination method is used for solution,whose computational complexity is O(M^(3)).The present method introduces a virtual body-fitted grid that moves together with the immersed boundary to overcome the above defect.As with the original implicit velocity correction-based IBM,the fractional step technique,which includes the prediction step and the correction step,is applied in the present method.Note that the correction step is implemented on the virtual grid in the present method instead of the Eulerian mesh in the original method.Since the relative positions between virtual grid points and Lagrangian points are changeless,the matrix in the correction step can be pre-calculated and stored,avoiding the need to update it at every time step.Although,within this approach,three additional steps including the marking virtual grid points and covered Eulerian points,and two interpolations between the Eulerian mesh and the virtual grid must be conducted at each time step,the computational effort is still greatly reduced as the computational complexity of these steps is O(M).A numerical experiment of flow around a transversely oscillating cylinder is first performed,demonstrating the improved efficiency,especially when the number of Lagrangian points is large.As validation,the flow over a flapping elliptical wing and a fluid-structure interaction(FSI)problem of vortex-induced vibrations of a circular cylinder are simulated.The numerical results are found to be in line with reference results,verifying the ability of the proposed method to simulate complex moving boundary problems.展开更多
This article firstly proposes two problems related to geological structure inversion with acoustic computed tomography (CT): ① the results surveyed are different from true stratum layers; ② the existing acoustic CT ...This article firstly proposes two problems related to geological structure inversion with acoustic computed tomography (CT): ① the results surveyed are different from true stratum layers; ② the existing acoustic CT inversion methods are based on wave's travel route and velocity analysis, which is short of comprehensive analysis of the revealed geological data. Then, it puts forward the method of applying the borehole data to revise acoustic CT investigation result through controlling the boundary velocity. This method comprehensively uses acoustic data and borehole data to invert the rock masses' shear wave speed. Comparing to calculating the rock mass' wave speed with acoustic data alone, it makes full use of the information, and the results obtained are closer to real stratum. Finally, it applies the method to engineering project and the results gotten with the method are more accurate, which shows the reliability and accuracy of the method.展开更多
Two-dimensional Navier-Stokes equations and energy equation governing incompressible laminar flow past a bundle of cylinders were numerically solved by using the finite element method. The velocity correction method w...Two-dimensional Navier-Stokes equations and energy equation governing incompressible laminar flow past a bundle of cylinders were numerically solved by using the finite element method. The velocity correction method was used for time advancement, and spatial discretization was carried out with the Galerkin weighted residual method. Viscous flows past the cylinder banks arranged in in-line cylinder bundles and staggered cylinder bundles, coupled with heat transfer, were investigated for pitch-diameter ratios of 1.5 and 2.0 and the Reynolds numbers from 50 to 500. Flow structures and heat transfer behavior were discussed. The results obtained agree well with available numerical data.展开更多
For two-dimensional wa ter flow in open channel, by discritizing hydrodynamic differential equation of conservative form, the corresponding algebraic equations were derived which invo lve the relationship between vel...For two-dimensional wa ter flow in open channel, by discritizing hydrodynamic differential equation of conservative form, the corresponding algebraic equations were derived which invo lve the relationship between velocity and depth. Based on the relationship, this paper deduced a modified formula of velocity correction for SIMPLE algorithm. A s a test case, the flow in a prismatic channel with two different slopes was com puted and a good result was obtained.展开更多
A boundary condition-implemented immersed boundary-lattice Boltzmann method(IB-LBM)is presented in this work.The present approach is an improvement to the conventional IB-LBM.In the conventional IB-LBM,the no-slip bou...A boundary condition-implemented immersed boundary-lattice Boltzmann method(IB-LBM)is presented in this work.The present approach is an improvement to the conventional IB-LBM.In the conventional IB-LBM,the no-slip boundary condition is only approximately satisfied.As a result,there is flow penetration to the solid boundary.Another drawback of conventional IB-LBM is the use of Dirac delta function interpolation,which only has the first order of accuracy.In this work,the no-slip boundary condition is directly implemented,and used to correct the velocity at two adjacent mesh points from both sides of the boundary point.The velocity correction is made through the second-order polynomial interpolation rather than the first-order delta function interpolation.Obviously,the two drawbacks of conventional IB-LBM are removed in the present study.Another important contribution of this paper is to present a simple way to compute the hydrodynamic forces on the boundary from Newton’s second law.To validate the proposed method,the two-dimensional vortex decaying problem and incompressible flow over a circular cylinder are simulated.As shown in the present results,the flow penetration problem is eliminated,and the obtained results compare very well with available data in the literature.展开更多
基金supported by the National Natural Science Foundation of China(Nos.92271103 and 12202191)the Natural Science Foundation of Jiangsu Province(No.BK20210273)+2 种基金Fund of the Prospective Layout of Scientific Research for NUAA(Nanjing University of Aeronautics and Astronautics)Fundamental Research Funds for the Central Universitiesthe Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘In this work,a virtual body-fitted grid is introduced and combined with the implicit velocity correction-based immersed boundary method(IBM)for simulation of incompressible flows with moving boundaries.The original implicit velocity correction-based IBM to this kind of problem requires the matrix inversion operation to be repeated at each time step,resulting in significant computational resources and time when the Gaussian elimination method is used for solution,whose computational complexity is O(M^(3)).The present method introduces a virtual body-fitted grid that moves together with the immersed boundary to overcome the above defect.As with the original implicit velocity correction-based IBM,the fractional step technique,which includes the prediction step and the correction step,is applied in the present method.Note that the correction step is implemented on the virtual grid in the present method instead of the Eulerian mesh in the original method.Since the relative positions between virtual grid points and Lagrangian points are changeless,the matrix in the correction step can be pre-calculated and stored,avoiding the need to update it at every time step.Although,within this approach,three additional steps including the marking virtual grid points and covered Eulerian points,and two interpolations between the Eulerian mesh and the virtual grid must be conducted at each time step,the computational effort is still greatly reduced as the computational complexity of these steps is O(M).A numerical experiment of flow around a transversely oscillating cylinder is first performed,demonstrating the improved efficiency,especially when the number of Lagrangian points is large.As validation,the flow over a flapping elliptical wing and a fluid-structure interaction(FSI)problem of vortex-induced vibrations of a circular cylinder are simulated.The numerical results are found to be in line with reference results,verifying the ability of the proposed method to simulate complex moving boundary problems.
文摘This article firstly proposes two problems related to geological structure inversion with acoustic computed tomography (CT): ① the results surveyed are different from true stratum layers; ② the existing acoustic CT inversion methods are based on wave's travel route and velocity analysis, which is short of comprehensive analysis of the revealed geological data. Then, it puts forward the method of applying the borehole data to revise acoustic CT investigation result through controlling the boundary velocity. This method comprehensively uses acoustic data and borehole data to invert the rock masses' shear wave speed. Comparing to calculating the rock mass' wave speed with acoustic data alone, it makes full use of the information, and the results obtained are closer to real stratum. Finally, it applies the method to engineering project and the results gotten with the method are more accurate, which shows the reliability and accuracy of the method.
基金The project supported by the Natural Science Foundation of China.(No.19889210)
文摘Two-dimensional Navier-Stokes equations and energy equation governing incompressible laminar flow past a bundle of cylinders were numerically solved by using the finite element method. The velocity correction method was used for time advancement, and spatial discretization was carried out with the Galerkin weighted residual method. Viscous flows past the cylinder banks arranged in in-line cylinder bundles and staggered cylinder bundles, coupled with heat transfer, were investigated for pitch-diameter ratios of 1.5 and 2.0 and the Reynolds numbers from 50 to 500. Flow structures and heat transfer behavior were discussed. The results obtained agree well with available numerical data.
文摘For two-dimensional wa ter flow in open channel, by discritizing hydrodynamic differential equation of conservative form, the corresponding algebraic equations were derived which invo lve the relationship between velocity and depth. Based on the relationship, this paper deduced a modified formula of velocity correction for SIMPLE algorithm. A s a test case, the flow in a prismatic channel with two different slopes was com puted and a good result was obtained.
基金supported by the National Natural Science Foundation of China(11272153).
文摘A boundary condition-implemented immersed boundary-lattice Boltzmann method(IB-LBM)is presented in this work.The present approach is an improvement to the conventional IB-LBM.In the conventional IB-LBM,the no-slip boundary condition is only approximately satisfied.As a result,there is flow penetration to the solid boundary.Another drawback of conventional IB-LBM is the use of Dirac delta function interpolation,which only has the first order of accuracy.In this work,the no-slip boundary condition is directly implemented,and used to correct the velocity at two adjacent mesh points from both sides of the boundary point.The velocity correction is made through the second-order polynomial interpolation rather than the first-order delta function interpolation.Obviously,the two drawbacks of conventional IB-LBM are removed in the present study.Another important contribution of this paper is to present a simple way to compute the hydrodynamic forces on the boundary from Newton’s second law.To validate the proposed method,the two-dimensional vortex decaying problem and incompressible flow over a circular cylinder are simulated.As shown in the present results,the flow penetration problem is eliminated,and the obtained results compare very well with available data in the literature.
