Mesh Metric
Mesh Metric
2010-01-12
1
By Eric
Element Quality
Element Quality
Element Quality
t Q lit
El
This metric is based on the ratio of the volume to the edge length for a
given element.
Range: 0 – 1
Rule: 见下图。 1最好,0最差。
网格体积为0或者
为负体积
0
差
正方体网格
1
好
2010-01-12
2
By Eric
Aspect Ratio(Triangles)
Aspect Ratio(Triangles)
Aspect Ratio for Triangles
T i
l
t R ti
A
Method:
f
从三角形的一个顶点引出对边的中线,
另外两边中点相连 构成线段KR ST
另外两边中点相连,构成线段KR,ST
分别做2个矩形如下:以中线ST为平行线,
分别过点R、K构造矩形两条对边,另外
两条对边分别过点S、T;以中线RK为平
行线 分别过点S T构造矩形两条对边
行线,分别过点S、T构造矩形两条对边,
另两条对边分别过点R、K
对另外两个顶点也如上面步骤做矩形,
共6个矩形
找出各矩形长边与短边之比并开立方
找出各矩形长边与短边之比并开立方,
数值最大者即为该三角形的Aspect Ratio
Rules:
Best triangle aspect ratio: 1
2010-01-12
3
By Eric
Aspect Ratio (Quadrilaterals)
Aspect Ratio (Quadrilaterals)
Aspect Ratio Calculation for Quadilaterals
l
f Q dil t
t R ti C l
l ti
A
Method:
如果单元不在一个平面上,各个节点将被投影到节点坐标平均值所在的平面上
画出两条矩形对边中点的连线,相交于一点O
以交点O为中心,分别过4个中点构造2个矩形。
找出两个矩形长边和短边之比的最大值,即为四边形的Aspect Ratio。
最 ,即为 形
个 形
和
p
Rule:
矩形网格最佳边长比为1,即该矩形为正方形。
2010-01-12
4
By Eric
Jacobian Ratio (1)
Jacobian Ratio (1)
bi
J
R ti
Jacobian Ratio
适应性较广,一般用于处理带有中节点的单元。
Jacobian Ratio越高,说明单元的计算能力越差。
越高,说明单元的计算能力越差。
Rule:
计算单元内个样本点雅克比矩阵的行列式值Rj
雅克比值(Jacobian Ratio)是样本点中行列式最大值与最小值的比值
雅克比值(Jacobian Ratio)是样本点中行列式最大值与最小值的比值
若两者正负号不同,雅克比值将为-100——该单元不可接受。
* 三角形单元的雅克比值
* A triangle or tetrahedron has a Jacobian ratio of 1 if each midside node, if any, is
positioned at the average of the corresponding corner node locations.
* This is true no matter how otherwise distorted the element may be.
2010-01-12
5
By Eric
Jacobian Ratio (2)
Jacobian Ratio (2)
四边形单元的雅克比值:
四边形单元的雅克比值
Any rectangle or rectangular
d
parallelepiped having no midside
t
nodes, or having midside nodes at
the midpoints of its edges, has a
Jacobian ratio of 1.
h i g
id id
d
Moving midside nodes toward or
Moving midside nodes toward or
away from each other can increase
the Jacobian ratio.
六面体单元雅克比值:
六面体单元雅克比值
A quadrilateral or brick has a
Jacobian ratio of 1 if
l
i
ll
ll
( ) i
(a) its opposing faces are all parallel to
f
each other, and
(b) each midside node, if any, is
positioned at the average of the
corresponding corner node locations.
corresponding corner node locations.
2010-01-12
6
By Eric
Warping Factor
Warping Factor
Warping factor
W i
Computed and tested for some quadrilateral shell elements, and the
t
f
quadrilateral faces of bricks, wedges, and pyramids.
A high factor may indicate a condition the underlying element formulation
cannot handle well, or may simply hint at a mesh generation flaw.
Rule:
Rule:
Best: 0 (此时为平面,无扭曲) 3D网格的扭曲系数
分别比较六个面的扭曲系数,取最大值
2010-01-12
7
d 45° l ti
Twisting the top face of a unit cube by 22.5°
and 45° relative to the base produces
warping factors of about 0.2 and 0.4,
respectively.
th b
d
t
By Eric
Parallel Deviation
Parallel Deviation
Parallel Deviation
P
计算对边矢量的点积,通过点积中的余弦值求出最大的夹角,即平行偏
l D i ti
ll
差(Parallel Deviation)
Rule:平行偏差为0最好,此时两对边平行。
四边形单元的平行偏差比较(P
i )
四边形单元的平行偏差比较(Parallel Deviation)
l D i
ll
2010-01-12
8
By Eric