Received by :2002‐09‐27 ;Revised by :2003‐05‐28畅
Project supported by the Science and T echnology Funds of China
Academy of Engineering Physics (960691 ,
990677)畅
Corresponding authors :Feng Qijing
倡
(1965‐) ,Male ,Professor .
第21卷第4期
2004 年 8 月
计 算 力 学 学 报
Chinese Journal of Computational Mechanics
Vol .21 ,No .4
August 2004
文章编号 :1007‐4708(2004)04‐0412‐07
Interface calculations in numerical method
for Eulerian hydrodynamics
Feng Qijing
倡
,He Changjiang ,Zhang Min ,Liang Xianhong ,Zhang Shudao
(Laboratory of Computational Physics ,Institute of Applied Physics and Computational Mathematics ,Beijing 100088)
Abstract :The algorithm proposed in this paper can be used to deal with interface of mixed cell (including free surface cell) in re‐
mapping step of twostep 2‐d and 3‐d multi‐component Eulerian hydrodynamics numerical methods .In a mixed cell the interface
is regarded as a straight line in 2‐d problems or plane in 3‐d problems .The whole method is composed of three steps :(1) U‐
sing area fractions of eight cells in 2‐d problems or volume fractions of twenty six cells in 3‐d problems surrounding the mixed
cell to determine the normal orientation of the interface .(2) Determining the equation (
p
osition) of the interface with the area
fraction (2‐d) or volume fraction (3‐d) of the mixed cell .(3) Calculating the flux passing across the boundary of cell ,and area
fraction (2‐d) or volume fraction (3‐d) of cell at next time .In the last part of this paper ,some 2‐d and 3‐d results of calculation
in comparison with results of MEPH (simplified SLIC) are presented .
Key words :Euler ;interface ;2 dimension ;3 dimension
1 Introduction
The advantage of Eulerian method is the ability of
computing large deformation problems . But in multi‐
component problems ,it is difficult to describe the in‐
terface exactly .Therefore how to capture interfaces of
media more accurately is one of the key points of Eule‐
rian method . To keep track of interface in Eulerian
method ,early methods are Lagrangian marking point
method ,SLIC method
[1]
,MEPH method
[2]
etc .In re‐
cent years ,several methods have been developed ,e .
g
.
front tracking method
[3]
,level set method
[4]
,Youngs
method
[5‐7]
and so on .Among them ,Youngs method is
not necessary to remember history and enlarge memo‐
ry ,it can be used to calculate interface easily and more
accurately .
The algorithm proposed in this paper is formed in
the process of developing two‐dimen‐
sional and three ‐ dimensional Eulerian codes ,
combining the idea of Youngs method .Our numerical
method is a two‐step one ,first step is Lagrangian step ,
and the second is remapping step .This paper concerns
handling interface of mixed cell (including free‐surface
cell) in remapping step .Original Youngs method pays
attention to geometry properties ,w hereas our method
stresses on the topological properties of function .By
taking a simple “coordinate transformation” ,this meth‐
od can simplify logical relations ,computing formulae ,
and coding work .
2 Methodology
For 2‐d and 3‐d problems ,the w hole method con‐
sists of three parts .
2 .1 Two dimensional problem
We regard the interface in a mixed cell as a straight
line .
2 .1 .1 Determine the normal orientation of
interface in a mixed cell
The normal orientation of the interface can be de‐
termined by area fractions of eight cells surrounding the
mixed cell .According to the idea of Youngs method ,
the normal orientation is defined by
n=
楚
f
|楚
f
|
(1)
here ,
f
is area fraction .that is :