This paper investigates an efficient immersed boundary method(IBM)for multiple-core CPU machines with local grid refinement for the calculation of heat transfer between fluids and finite-sized particles.The fluid mome...This paper investigates an efficient immersed boundary method(IBM)for multiple-core CPU machines with local grid refinement for the calculation of heat transfer between fluids and finite-sized particles.The fluid momentum equations are solved by using the fractional step method,while the energy equation is solved by employing the second-order Adams-Bashforth method.For efficient load balancing between the CPU cores,the coupling between particles and fluid is obtained by applying the body force in the fluid equations,which depends on the solid volume fraction of particles contained in each grid cell,and then by linearly interpolating the particle temperature and velocity on the fluid grid cell(in place of the delta function commonly used in literature).Several test cases from the literature are studied,and good agreement is observed between the simulation results and the literature.Finally,a scaling study on multiple core machines is performed,demonstrating the proposed IBM's capabilities for a significant reduction in processing time.展开更多
The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric con...The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric constants between insulation paper and transformer oil,restricted the development of transformer with smaller size and larger capacity.In view of this situation and the transformer’s demand for the dielectric physicochemical and mechanical property of insulation material,polycarbonate,polyester film and polyphenylene sulfide with high high-temperature resistance were chosen for the comparison analysis in this paper We did the 300-day thermal aging experiment on four samples in transformer oil under different aging temperatures of90°C,110°C and 130°C,then analyzed the changes of their dielectric properties.The experiment results are as follows;the permittivity and dielectric dissipation factor of the three polymer materials are apparently smaller than those of the paper both before and after 300-day aging;the volume resistivity and partial discharge inception voltage of the three materials are higher than those of the paper both before and after aging;and the breakdown field strength of polycarbonate is higher than that of the paper both before and after aging,while that of polyester film and polyphenylene sulfide are slightly lower than that of the paper.展开更多
In this paper,a mathematical model is developed to study the wave propagation in an infinite,homogeneous,transversely isotropic thermo-piezoelectric solid bar of circular cross-sections immersed in inviscid fluid.The ...In this paper,a mathematical model is developed to study the wave propagation in an infinite,homogeneous,transversely isotropic thermo-piezoelectric solid bar of circular cross-sections immersed in inviscid fluid.The present study is based on the use of the three-dimensional theory of elasticity.Three displacement potential functions are introduced to uncouple the equations of motion and the heat and electric conductions.The frequency equations are obtained for longitudinal and flexural modes of vibration and are studied based on Lord-Shulman,Green-Lindsay and Classical theory theories of thermo elasticity.The frequency equations of the coupled system consisting of cylinder and fluid are developed under the assumption of perfectslip boundary conditions at the fluid-solid interfaces,which are obtained for longitudinal and flexural modes of vibration and are studied numerically for PZT-4 material bar immersed in fluid.The computed non-dimensional frequencies are compared with Lord-Shulman,Green-Lindsay and Classical theory theories of thermo elasticity for longitudinal and flexural modes of vibrations.The dispersion curves are drawn for longitudinal and flexural modes of vibrations.Moreover,the dispersion of specific loss and damping factors are also analyzed for longitudinal and flexural modes of vibrations.展开更多
In this paper,numerical sensitivity analysis with respect to the Reynolds number for the flow past obstacle problem is presented.To carry out such analysis,at each time step,we need to solve the incompressible Navier-...In this paper,numerical sensitivity analysis with respect to the Reynolds number for the flow past obstacle problem is presented.To carry out such analysis,at each time step,we need to solve the incompressible Navier-Stokes equations on irregular domains twice,one for the primary variables;the other is for the sensitivity variables with homogeneous boundary conditions.The Navier-Stokes solver is the augmented immersed interface method for Navier-Stokes equations on irregular domains.One of the most important contribution of this paper is that our analysis can predict the critical Reynolds number at which the vortex shading begins to develop in the wake of the obstacle.Some interesting experiments are shown to illustrate how the critical Reynolds number varies with different geometric settings.展开更多
Dynamic fluid-solid interactions are widely found in chemical engineering, such as in particle-laden flows, which usually contain complex moving boundaries. The immersed boundary method （IBM） is a convenient approac...Dynamic fluid-solid interactions are widely found in chemical engineering, such as in particle-laden flows, which usually contain complex moving boundaries. The immersed boundary method （IBM） is a convenient approach to handle fluid-solid interactions with complex geometries. In this work, Uhlmann＇s direct-forcing IBM is improved and implemented on a supercomputer with CPU-GPU hybrid architec- ture. The direct-forcing IBM is modified as follows： the Poisson＇s equation for pressure is solved before evaluation of the body force, and the force is only distributed to the Cartesian grids inside the immersed boundary. A multidirect forcing scheme is used to evaluate the body force. These modifications result in a divergence-free flow field in the fluid domain and the no-slip boundary condition at the immersed boundary simultaneously. This method is implemented in an explicit finite-difference fractional-step scheme, and validated by 2D simulations of lid-driven cavity flow, Couette flow between two concentric cylinders and flow over a circular cylinder. Finally, the method is used to simulate the sedimentation of two circular particles in a channel. The results agree very well with previous experimental and numerical data, and are more accurate than the conventional direct-forcing method, especially in the vicinity of a moving boundary.展开更多
文摘This paper investigates an efficient immersed boundary method(IBM)for multiple-core CPU machines with local grid refinement for the calculation of heat transfer between fluids and finite-sized particles.The fluid momentum equations are solved by using the fractional step method,while the energy equation is solved by employing the second-order Adams-Bashforth method.For efficient load balancing between the CPU cores,the coupling between particles and fluid is obtained by applying the body force in the fluid equations,which depends on the solid volume fraction of particles contained in each grid cell,and then by linearly interpolating the particle temperature and velocity on the fluid grid cell(in place of the delta function commonly used in literature).Several test cases from the literature are studied,and good agreement is observed between the simulation results and the literature.Finally,a scaling study on multiple core machines is performed,demonstrating the proposed IBM's capabilities for a significant reduction in processing time.
基金supported by the National Natural Science Foundation of China(Grant No.50977025)
文摘The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric constants between insulation paper and transformer oil,restricted the development of transformer with smaller size and larger capacity.In view of this situation and the transformer’s demand for the dielectric physicochemical and mechanical property of insulation material,polycarbonate,polyester film and polyphenylene sulfide with high high-temperature resistance were chosen for the comparison analysis in this paper We did the 300-day thermal aging experiment on four samples in transformer oil under different aging temperatures of90°C,110°C and 130°C,then analyzed the changes of their dielectric properties.The experiment results are as follows;the permittivity and dielectric dissipation factor of the three polymer materials are apparently smaller than those of the paper both before and after 300-day aging;the volume resistivity and partial discharge inception voltage of the three materials are higher than those of the paper both before and after aging;and the breakdown field strength of polycarbonate is higher than that of the paper both before and after aging,while that of polyester film and polyphenylene sulfide are slightly lower than that of the paper.
文摘In this paper,a mathematical model is developed to study the wave propagation in an infinite,homogeneous,transversely isotropic thermo-piezoelectric solid bar of circular cross-sections immersed in inviscid fluid.The present study is based on the use of the three-dimensional theory of elasticity.Three displacement potential functions are introduced to uncouple the equations of motion and the heat and electric conductions.The frequency equations are obtained for longitudinal and flexural modes of vibration and are studied based on Lord-Shulman,Green-Lindsay and Classical theory theories of thermo elasticity.The frequency equations of the coupled system consisting of cylinder and fluid are developed under the assumption of perfectslip boundary conditions at the fluid-solid interfaces,which are obtained for longitudinal and flexural modes of vibration and are studied numerically for PZT-4 material bar immersed in fluid.The computed non-dimensional frequencies are compared with Lord-Shulman,Green-Lindsay and Classical theory theories of thermo elasticity for longitudinal and flexural modes of vibrations.The dispersion curves are drawn for longitudinal and flexural modes of vibrations.Moreover,the dispersion of specific loss and damping factors are also analyzed for longitudinal and flexural modes of vibrations.
基金The first and second authors are partially supported by US-ARO grant 49308-MAUS-AFSOR grant FA9550-06-1-0241+2 种基金The second author is also partially supported by US-NSF grant DMS-0911434the US-NIH grant 096195-01,and CNSF 11071123The third author is partially supported by the Hong Kong RGC Grant HKBU201710。
文摘In this paper,numerical sensitivity analysis with respect to the Reynolds number for the flow past obstacle problem is presented.To carry out such analysis,at each time step,we need to solve the incompressible Navier-Stokes equations on irregular domains twice,one for the primary variables;the other is for the sensitivity variables with homogeneous boundary conditions.The Navier-Stokes solver is the augmented immersed interface method for Navier-Stokes equations on irregular domains.One of the most important contribution of this paper is that our analysis can predict the critical Reynolds number at which the vortex shading begins to develop in the wake of the obstacle.Some interesting experiments are shown to illustrate how the critical Reynolds number varies with different geometric settings.
基金supported by the National Natural Science Foundation of China(NSFC) under Grant Nos.21225628,51106168 and 11272312the "Strategic Priority Research Program" of Chinese Academy of Sciences(CAS) under Grant No.XDA07080102
文摘Dynamic fluid-solid interactions are widely found in chemical engineering, such as in particle-laden flows, which usually contain complex moving boundaries. The immersed boundary method （IBM） is a convenient approach to handle fluid-solid interactions with complex geometries. In this work, Uhlmann＇s direct-forcing IBM is improved and implemented on a supercomputer with CPU-GPU hybrid architec- ture. The direct-forcing IBM is modified as follows： the Poisson＇s equation for pressure is solved before evaluation of the body force, and the force is only distributed to the Cartesian grids inside the immersed boundary. A multidirect forcing scheme is used to evaluate the body force. These modifications result in a divergence-free flow field in the fluid domain and the no-slip boundary condition at the immersed boundary simultaneously. This method is implemented in an explicit finite-difference fractional-step scheme, and validated by 2D simulations of lid-driven cavity flow, Couette flow between two concentric cylinders and flow over a circular cylinder. Finally, the method is used to simulate the sedimentation of two circular particles in a channel. The results agree very well with previous experimental and numerical data, and are more accurate than the conventional direct-forcing method, especially in the vicinity of a moving boundary.
