Qiang Sun | RMIT University (original) (raw)

Papers by Qiang Sun

A boundary integral formulation of electromagnetics that involves only the components of E and H ... more A boundary integral formulation of electromagnetics that involves only the components of E and H is derived without the use of surface currents that appear in the classical Poggio and Miller, Chang and Harrington, and Wu and Tsai formulation. The kernels of the boundary integral equations for E and H are nonsingular so that all field quantities at the surface can be determined to high precision and also geometries with closely spaced surfaces present no numerical difficulties. Quadratic elements can readily be used to represent the surfaces so that the surface integrals can be calculated to higher numerical precision than using planar elements for the same numbers of degrees of freedom.

A boundary integral formulation for the solution of the Helmholtz equation is developed in which ... more A boundary integral formulation for the solution of the Helmholtz equation is developed in which all traditional singular behaviour in the boundary integrals is removed analytically. The numerical precision of this approach is illustrated with calculation of the pressure field owing to radiating bodies in acoustic wave problems. This method facilitates the use of higher order surface elements to represent boundaries, resulting in a significant reduction in the problem size with improved precision. Problems with extreme geometric aspect ratios can also be handled without diminished precision. When combined with the CHIEF method, uniqueness of the solution of the exterior acoustic problem is assured without the need to solve hypersingular integrals.

A non-singular formulation of the boundary integral method (BIM) is presented for the Laplace equ... more A non-singular formulation of the boundary integral method (BIM) is presented for the Laplace equation whereby the well-known singularities that arise from the fundamental solution are eliminated analytically. A key advantage of this approach is that numerical errors that arise due to the proximity of nodes located on osculating boundaries are suppressed. This is particularly relevant in multi-scale problems where high accuracy is required without undue increase in computational cost when the spacing between boundaries become much smaller than their characteristic dimensions. The elimination of the singularities means that standard quadrature can be used to evaluate the surface integrals and this results in about 60% savings in coding effort. The new formulation also affords a numerically robust way to calculate the potential close to the boundaries. Detailed implementations of this approach are illustrated with problems involving osculating boundaries, 2D domains with corners and a wave drag problem in a 3D semi-infinite domain. The explicit formulation of problems with axial symmetry is also given.

We study the forces and torques experienced by pill-shaped Janus particles of different aspect ra... more We study the forces and torques experienced by pill-shaped Janus particles of different aspect ratios where half of the surface obeys the no-slip boundary condition and the other half obeys the Navier slip condition of varying slip lengths. Using a recently developed boundary integral formulation whereby the traditional singular behavior of this approach is removed analytically, we quantify the strength of the forces and torques experienced by such particles in a uniform flow field in the Stokes regime. Depending on the aspect ratio and the slip length, the force transverse to the flow direction can change sign. This is a novel property unique to the Janus nature of the particles.

A mathematical model and a numerical solution procedure are developed to simulate flow field thro... more A mathematical model and a numerical solution procedure are developed to simulate flow field through a 3D permeable vessel with multibranches embedded in a solid tumour. The model is based on Poisseuille's law for the description of the flow through the vessels, Darcy's law for the fluid field inside the tumour interstitium, and Starling's law for the flux transmitted across the vascular walls. The solution procedure is based on a coupled method, in which the finite difference method is used for the flow in the vessels and the boundary element method is used for the flow in the tumour. When vessels meet each other at a junction, the pressure continuity and mass conservation are imposed at the junction. Three typical representative structures within the tumour vasculature, symmetrical dichotomous branching, asymmetrical bifurcation with uneven radius of daughter vessels and trifurcation, are investigated in detail as case studies. These results have demonstrated the features of tumour flow environment by the pressure distributions and flow velocity field.

A formulation of the boundary integral method for solving partial differential equations has been... more A formulation of the boundary integral method for solving partial differential equations has been developed whereby the usual weakly singular integral and the Cauchy principal value integral can be removed analytically. The broad applicability of the approach is illustrated with a number of problems of practical interest to fluid and continuum mechanics including the solution of the Laplace equation for potential flow, the Helmholtz equation as well as the equations for Stokes flow and linear elasticity.

Steady-state free convection heat transfer behavior of nanofluids is investigated numerically ins... more Steady-state free convection heat transfer behavior of nanofluids is investigated numerically inside a right-angle triangular enclosure filled with a porous medium. The flush mounted heater with finite size is placed on the left vertical wall. The temperature of the inclined wall is lower than the heater, and the rest of walls are adiabatic. The governing equations are obtained based on the Darcy’s law and the nanofluid model proposed by Tiwari and Das [1]. The transformed dimensionless governing equations were solved by finite difference method and solution for algebraic equations was obtained through Successive Under Relaxation method. Investigations with three types of nanofluids were made for different values of Rayleigh number Ra of a porous medium with the range of 10 ≤ Ra ≤ 1000, size of heater Ht as 0.1 ≤ Ht ≤ 0.9, position of heater Yp when 0.25 ≤ Yp ≤ 0.75, enclosure aspect ratio AR as 0.5 ≤ AR ≤ 1.5 and solid volume fraction parameter ϕ of nanofluids with the range of 0.0 ≤ ϕ ≤ 0.2. It is found that the maximum value of average Nusselt number is obtained by decreasing the enclosure aspect ratio and lowering the heater position with the highest value of Rayleigh number and the largest size of heater. It is further observed that the heat transfer in the cavity is improved with the increasing of solid volume fraction parameter of nanofluids at low Rayleigh number, but opposite effects appear when the Rayleigh number is high.

New Trends in Fluid Mechanics Research, 2009

The blood flow through a single cuvered permeable tube in a solid tumour is simulated in this wor... more The blood flow through a single cuvered permeable tube in a solid tumour is simulated in this work. This is extented from the analysis for a straight tube and it lays down the foundation for further work on a network of tubes or tubes with branches in tumours.

"An analytic technique, namely the homotopy analysis method, is applied to solve the nonlinear t... more "An analytic technique, namely the homotopy analysis method, is applied to solve the nonlinear travelling waves governed by the Klein–Gordon equation. The phase speed and the solution, which are dependent on the amplitude a, are given and valid in the whole
region"

本文首先介绍了基于有限元疲劳寿命的理论基础和分析方法,然后建立锥柱结合壳有限元分析模型,经计算,疲劳寿命结果与试验数据相符,而局部应力-应变法估算的疲劳寿命误差较大.本文最后得出用有限元方法估算... more 本文首先介绍了基于有限元疲劳寿命的理论基础和分析方法,然后建立锥柱结合壳有限元分析模型,经计算,疲劳寿命结果与试验数据相符,而局部应力-应变法估算的疲劳寿命误差较大.本文最后得出用有限元方法估算疲劳寿命不但可靠度高,而且可以方便地修改计算参数,进行结构优化,提高了计算的准确性和运算效率,极大程度地降低了人工费用.

A boundary integral formulation of electromagnetics that involves only the components of E and H ... more A boundary integral formulation of electromagnetics that involves only the components of E and H is derived without the use of surface currents that appear in the classical Poggio and Miller, Chang and Harrington, and Wu and Tsai formulation. The kernels of the boundary integral equations for E and H are nonsingular so that all field quantities at the surface can be determined to high precision and also geometries with closely spaced surfaces present no numerical difficulties. Quadratic elements can readily be used to represent the surfaces so that the surface integrals can be calculated to higher numerical precision than using planar elements for the same numbers of degrees of freedom.

A boundary integral formulation for the solution of the Helmholtz equation is developed in which ... more A boundary integral formulation for the solution of the Helmholtz equation is developed in which all traditional singular behaviour in the boundary integrals is removed analytically. The numerical precision of this approach is illustrated with calculation of the pressure field owing to radiating bodies in acoustic wave problems. This method facilitates the use of higher order surface elements to represent boundaries, resulting in a significant reduction in the problem size with improved precision. Problems with extreme geometric aspect ratios can also be handled without diminished precision. When combined with the CHIEF method, uniqueness of the solution of the exterior acoustic problem is assured without the need to solve hypersingular integrals.

A non-singular formulation of the boundary integral method (BIM) is presented for the Laplace equ... more A non-singular formulation of the boundary integral method (BIM) is presented for the Laplace equation whereby the well-known singularities that arise from the fundamental solution are eliminated analytically. A key advantage of this approach is that numerical errors that arise due to the proximity of nodes located on osculating boundaries are suppressed. This is particularly relevant in multi-scale problems where high accuracy is required without undue increase in computational cost when the spacing between boundaries become much smaller than their characteristic dimensions. The elimination of the singularities means that standard quadrature can be used to evaluate the surface integrals and this results in about 60% savings in coding effort. The new formulation also affords a numerically robust way to calculate the potential close to the boundaries. Detailed implementations of this approach are illustrated with problems involving osculating boundaries, 2D domains with corners and a wave drag problem in a 3D semi-infinite domain. The explicit formulation of problems with axial symmetry is also given.

We study the forces and torques experienced by pill-shaped Janus particles of different aspect ra... more We study the forces and torques experienced by pill-shaped Janus particles of different aspect ratios where half of the surface obeys the no-slip boundary condition and the other half obeys the Navier slip condition of varying slip lengths. Using a recently developed boundary integral formulation whereby the traditional singular behavior of this approach is removed analytically, we quantify the strength of the forces and torques experienced by such particles in a uniform flow field in the Stokes regime. Depending on the aspect ratio and the slip length, the force transverse to the flow direction can change sign. This is a novel property unique to the Janus nature of the particles.

A mathematical model and a numerical solution procedure are developed to simulate flow field thro... more A mathematical model and a numerical solution procedure are developed to simulate flow field through a 3D permeable vessel with multibranches embedded in a solid tumour. The model is based on Poisseuille's law for the description of the flow through the vessels, Darcy's law for the fluid field inside the tumour interstitium, and Starling's law for the flux transmitted across the vascular walls. The solution procedure is based on a coupled method, in which the finite difference method is used for the flow in the vessels and the boundary element method is used for the flow in the tumour. When vessels meet each other at a junction, the pressure continuity and mass conservation are imposed at the junction. Three typical representative structures within the tumour vasculature, symmetrical dichotomous branching, asymmetrical bifurcation with uneven radius of daughter vessels and trifurcation, are investigated in detail as case studies. These results have demonstrated the features of tumour flow environment by the pressure distributions and flow velocity field.

A formulation of the boundary integral method for solving partial differential equations has been... more A formulation of the boundary integral method for solving partial differential equations has been developed whereby the usual weakly singular integral and the Cauchy principal value integral can be removed analytically. The broad applicability of the approach is illustrated with a number of problems of practical interest to fluid and continuum mechanics including the solution of the Laplace equation for potential flow, the Helmholtz equation as well as the equations for Stokes flow and linear elasticity.

Steady-state free convection heat transfer behavior of nanofluids is investigated numerically ins... more Steady-state free convection heat transfer behavior of nanofluids is investigated numerically inside a right-angle triangular enclosure filled with a porous medium. The flush mounted heater with finite size is placed on the left vertical wall. The temperature of the inclined wall is lower than the heater, and the rest of walls are adiabatic. The governing equations are obtained based on the Darcy’s law and the nanofluid model proposed by Tiwari and Das [1]. The transformed dimensionless governing equations were solved by finite difference method and solution for algebraic equations was obtained through Successive Under Relaxation method. Investigations with three types of nanofluids were made for different values of Rayleigh number Ra of a porous medium with the range of 10 ≤ Ra ≤ 1000, size of heater Ht as 0.1 ≤ Ht ≤ 0.9, position of heater Yp when 0.25 ≤ Yp ≤ 0.75, enclosure aspect ratio AR as 0.5 ≤ AR ≤ 1.5 and solid volume fraction parameter ϕ of nanofluids with the range of 0.0 ≤ ϕ ≤ 0.2. It is found that the maximum value of average Nusselt number is obtained by decreasing the enclosure aspect ratio and lowering the heater position with the highest value of Rayleigh number and the largest size of heater. It is further observed that the heat transfer in the cavity is improved with the increasing of solid volume fraction parameter of nanofluids at low Rayleigh number, but opposite effects appear when the Rayleigh number is high.

New Trends in Fluid Mechanics Research, 2009

The blood flow through a single cuvered permeable tube in a solid tumour is simulated in this wor... more The blood flow through a single cuvered permeable tube in a solid tumour is simulated in this work. This is extented from the analysis for a straight tube and it lays down the foundation for further work on a network of tubes or tubes with branches in tumours.

"An analytic technique, namely the homotopy analysis method, is applied to solve the nonlinear t... more "An analytic technique, namely the homotopy analysis method, is applied to solve the nonlinear travelling waves governed by the Klein–Gordon equation. The phase speed and the solution, which are dependent on the amplitude a, are given and valid in the whole
region"

本文首先介绍了基于有限元疲劳寿命的理论基础和分析方法,然后建立锥柱结合壳有限元分析模型,经计算,疲劳寿命结果与试验数据相符,而局部应力-应变法估算的疲劳寿命误差较大.本文最后得出用有限元方法估算... more 本文首先介绍了基于有限元疲劳寿命的理论基础和分析方法,然后建立锥柱结合壳有限元分析模型,经计算,疲劳寿命结果与试验数据相符,而局部应力-应变法估算的疲劳寿命误差较大.本文最后得出用有限元方法估算疲劳寿命不但可靠度高,而且可以方便地修改计算参数,进行结构优化,提高了计算的准确性和运算效率,极大程度地降低了人工费用.