Negative elements

vijaykamesh · April 26, 2016, 08:58

Hello,

I'm meshing a tidal turbine in Icem with two domain. I done with the meshing and i checked the mesh quality by det 2x2x2. It showing a negative values, i.e. bad elements (few) around the hub part. I checked the elements there but it looks fine. The both sides of the hub mesh is almost similar. The edge spacing and nodes are almost similar. The other side of the hub is not having any bad elements like this. I dont know how to fix it. Please see the pics. Third picture is mesh on the other side of the hub which dont have any bad elements.

alirezame · April 27, 2016, 04:06

Hello,
have you checked the orientation of the surfaces? x=i, y=j and z=k
I have not worked with ICEM but in all of the meshing codes there should be possible to define or change the orientation of surfaces or zones.

davidwilcox · April 27, 2016, 23:54

i encountered this lots of time. The way i solved it is to first highlight the areas of negative determinants. Then what i normally do is move the points connecting the edges ( not curves!) around that area. I said edges because i'm assuming you are doing the blocking method. this is very common if you have twists in the geometry.

vijaykamesh · April 28, 2016, 08:54

Yeah, I'm doing structure mesh. I understand that you meant vertices. I tried already by moving vertices, changing nodes and spacing but nothing improves here. The hub part is little complex in geometry and I'm using low y+ values so first cell distance is 6.7e-6 m. The bad elements also forming for first two layers from the surface. if i increase the first cell distance the number of bad elements(negative values) are reduced but not completely removed. I zoomed the elements and i see there is overlapping of cells (not sure). If its overlapping of cells means how it can be rectified.

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April 27, 2016, 04:06		#2
alirezame Member Join Date: Nov 2013 Posts: 57 Rep Power: 13	Hello, have you checked the orientation of the surfaces? x=i, y=j and z=k I have not worked with ICEM but in all of the meshing codes there should be possible to define or change the orientation of surfaces or zones.

April 27, 2016, 23:54		#3
davidwilcox Senior Member david Join Date: Oct 2012 Posts: 142 Rep Power: 14	i encountered this lots of time. The way i solved it is to first highlight the areas of negative determinants. Then what i normally do is move the points connecting the edges ( not curves!) around that area. I said edges because i'm assuming you are doing the blocking method. this is very common if you have twists in the geometry.

April 28, 2016, 08:54		#4
vijaykamesh New Member vijaykamesh Join Date: Dec 2015 Posts: 12 Rep Power: 10	Yeah, I'm doing structure mesh. I understand that you meant vertices. I tried already by moving vertices, changing nodes and spacing but nothing improves here. The hub part is little complex in geometry and I'm using low y+ values so first cell distance is 6.7e-6 m. The bad elements also forming for first two layers from the surface. if i increase the first cell distance the number of bad elements(negative values) are reduced but not completely removed. I zoomed the elements and i see there is overlapping of cells (not sure). If its overlapping of cells means how it can be rectified.