In Sep.2009, I will go to the University of Washington to further my study under the supervision of Prof. Anantram. My research interests include: Quantum Physics, Large-Scale Scientific Computation, Nanoelectronics, IC & Device Technology, etc.
papers published at Tsinghua University: (partial list)
Jie Liu, Jun Zou, Jihuan Tian, Jiansheng Yuan, ¡°Analysis of Electric Field, Ion Flow Density and Corona Loss of Same-Tower Double-Circuit HVDC Lines Using Improved FEM¡±, IEEE Transactions on Power Delivery, vol.24, issue.1, pp.482-483. <SCI source> (PDF, also available at IEEE Xplorer)
Jie Liu , Duo Chen, Jihuan Tian, Yun Xu, Jiansheng Yuan, ¡°Efficient Analysis of Electromagnetic Fields near Lightning Channel by Using SIBC in FDTD¡±, The 20th International Zurich Symposium on Electromagnetic Compatibility, Zurich, Switzerland, 2009 (EMC Zurich 2009), conf. proc. pp.129-132. (PDF, also available at IEEE Xplorer)
Jie Liu, Jun Zou, Jihuan Tian, Jiansheng Yuan, Xinshan Ma, ¡°An Accurate Adaptive Method to Draw 2-D Electric Lines of Force¡±, The 8th International Symposium on Antennas, Propagation and EM Theory, Kunming, China, 2008 (ISAPE 2008), conf. proc. pp.1092-1095. <EI source> (PDF)
Y. Yang, J. Liu , J. B. Lee, S. H. Chang, J. Zou, ¡°Field Calculation for HVDC Transmission Lines over Irregular Terrain Using an Adaptive Boundary Element Method with Fast Matrix Filling¡±, IEEE Conference on Electromagnetic Computation, Athens, Greece, 2008 (IEEE CEFC 2008). (PDF)
Research
(Master Thesis, 2007-2008) Topic and Background: Analysis of Ion Flow Field, Audible Noise, and Radio Interference of Same-Tower Double-Circuit High-Voltage Direct-Current (HVDC) Power Transmission lines. The high potential gradient near HVDC lines will ionize the ambient air (often referred to as "corona"), generating cationic and anionic charges. According to the advection-diffusion-reaction equation, these charges will be difted by electric field (E) into the space to form the spatial charge density (¦Ñ) . In turn, according to the Poisson equation, ¦Ñ will also change E. Therefore, ¦Ñ and E are calculated self-consistently here until convergence. After convergence, the ion current density (J) could be calculated by using ¦Ñ and E in the post-processing step. Excessive E and J will exert negative impact on the surrounding environment, so they need to be calculated and minimized while designing the HVDC projects.
This research project consists of two parts: (1) to analyze the ground-level E and J caused by the emerging
same-tower double-circuit HVDC lines by using iterative Finite Element Method; (2) to calculate audible noise and radio interference of the same-tower double-circuit HVDC lines by using Successive Image Method and empirical formulas.
(2008) Topic and Background:
Efficient Analysis of EM Field near the Lightning Channel. To simulate the transient electromagnetic fields caused by lightning,
the engineering models are widely used. In the engineering
models, the transient electromagnetic fields are calculated
from the vertical lightning channel current, whose waveform
is specified in advance according to the observed lightning
return-stroke characteristics. Sommerfeld integrals can be
used to numerically calculate this problem, but it is inefficient
unless some special approximations and tactics are applied. The ordinary
FDTD method could be applied do the
calculation. But it is extremely timeconsuming.
The ordinary FDTD method is inefficient because the conductive ground need to be discretized, so the spatial grid need to be very small. Which makes the situation worse is that the temporal grid also need to be corespondingly small to ensure the calculation stability. Here, Surface Impedance Boundary condition is applied to exclude the ground from the calculation domain. So the simulation efficency could be enhanced by more than 90%.
(2008) Topic and Background: Accurate Adaptive Method for Drawing 2-D Electric Lines of Force. The visualization of the electric lines of force is a very
important function of the post-processing module in
electromagnetic field analysis software packages.
The existing methods to draw the static electric lines of
force can be classified into two categories. The first category
is the Euler¡¯s method, which plots the electric lines of
force ahead by using the tangent direction of the electric field
at a certain point to approximate the direction of electric field
in the vicinity. The second category is the Complex Potential
Function (CPF) method, which plots the electric lines
of force by utilizing the mathematical property that the equivalue
lines of the imaginary part of the complex potential
function are the electric lines of force.
Euler¡¯s method is inaccurate, because using the tangent
direction of electric field to approximate the direction of
electric field in the nearby region generally leads to error,
especially in the region where the direction of electric field
changes rapidly.
The CPF method is accurate, but the program based on the
CPF method to draw electric lines of force in multiconnected
domain is difficult to implement and inefficient to
run.
Here, an adaptive method is proposed and implemented to improve the efficiency and precision. the procedure of the proposed method is similar to that of the Euler method. The difference is that the proposed method uses the high-order Taylor expansion formula to adaptively control the plotting length. So the proposed method could achieve higher accuracy, especially in the region where the electric potential changes rapidly.