Mei-Jiau Huang

Effect of the Temperature Dependence of Transmissivity on the Thermal Boundary Conductance Between Two Dissimilar Solids

The traditional diffuse mismatch model allows only elastic scattering processes and therefore underpredicts the thermal boundary conductance between two acoustically mismatched solids. To fix it, models that take inelastic scattering into consideration have been proposed. However, many of them do not take the contribution of the temperature derivative of the transmissivity into consideration; some allow phonons that are reflected by the interface in lower-level anharmonic phonon processes to further participate in higher-level ones, resulting in high transmissivity at elevated temperature. In this work, modifications are proposed to fix the above two drawbacks. Necessary physical assumptions are made clearly to distinguish the total energy flux and the participating energy flux associated with each level of processes. Agreement of the predictions with the experimental measurements is obtained by adjusting the ratio of these two fluxes.

A sub-cell spectral-element simulator for 2D rigid-body-fluid interaction problems

In this work, we propose an immersed-boundary-type simulation method for the two-way coupling problems between a rigid body and a fluid. In this simulation tool, the entire fluid-solid domain is treated as an incompressible fluid with non-uniform density and the no-slip boundary condition at the rigid body surface is enforced by the penalization method. The fluid solver is developed in use of the spectral element method for the spatial discretization and the mixed explicit/implicit scheme for the temporal discretization. An additional Lagrangian mesh is employed and attached to the rigid body in order to trace the rigid body and to perform the area integration over the solid domain. Besides, a so-called sub-cell scheme is developed to smooth the discontinuity at the fluid-solid interface. The validity and accuracy of the proposed simulation method were examined well by applying it to the sedimentation problems of circular, triangular, square, as well as elliptic cylinders in a channel. An accuracy of 2nd order was observed, probably due to the use of triangular Lagrangian elements and consequently a piecewise-linear approximation of the rigid body shape and also due to the 2nd-order interpolation involved in the sub-cell scheme.