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网格质量,提高网格质量的方法.pdf

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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
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