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lakers June 15, 2009 12:06

Continuative BC

what does the continuative and symmetry boundary condition mean?

i have defined two mesh block. one inside the other, i.e., the min/max for the two blocks are -

Block 1

X Direction :
Total Cells: 75
Fixed Point 1: -25
Fixed Point 2: 125

Y Direction :
Total Cells: 75
Fixed Point 1: -25
Fixed Point 2: 475

Z Direction :
Total Cells: 75
Fixed Point 1: -100
Fixed Point 2: 130

Block 2

X Direction :
Total Cells: 50
Fixed Point 1: 35
Fixed Point 2: 70

Y Direction :
Total Cells: 50
Fixed Point 1: 80
Fixed Point 2: 210

Z Direction :
Total Cells: 50
Fixed Point 1: -30
Fixed Point 2: 90

I have fined the mesh in the second block as there are very thin blades of a waterwheel in it. The water flows normally in the two blocks. So, my doubt is what boundary condition do I use for the second block? continuative or symmetry? or any other?

Also, in the first place, I am not sure whether my meshing is appropriate or not?

Please help!

melissa June 15, 2009 17:41

For nested mesh blocks it doesn't matter what you set as the boundary conditions they will reset to interlock boundaries automatically.

lakers June 15, 2009 18:12

Thank you so much melissa

i have one more doubt...
i want to solve a problem in which the axis of rotation of a waterwheel is continuously moving because the structure on which the waterwheel is resting is floating in water. how is is possible to define this to the software flow3d?
i hav activated the moving and deforming model. and activated the coupled motion. now, how do i define the rotation?

if i am not clear in the problem, then reply back...

melissa June 15, 2009 18:16

Meshing Geometry tab under component>Type of moving object>select edit. Initial/prescribed velocities. More info can be found in the manual from menu Help>Contents.

lakers June 16, 2009 06:48

sorry.. but that does not help me..

i'll try to explain my problem in more detail...
there is a structure on which a waterwheel is attached with the help of screws. the waterwheel is free to rotate. the structure will be kept in a river and will float on the river. due to the water current in the river, the water will go in between the structure through the water wheel, and hence, the waterwheel will rotate.

for the simulation of rotation of the waterwheel, i chose 'fixed x-axis rotation' in the 'motion constraints' of the 'moving object' model. i entered the initial y and z component of the axis of rotation. but as the structure is floating on water, these y and z components will continuously change... so how to define that in the problem?

lakers June 16, 2009 06:51

could a possible solution to the above problem be that i use the '6 degree of freedom' model instead of the 'fixed x-axis rotation' model?

stefmascio June 16, 2009 11:02

yes, you have to define: "coupled 6dof motion", and then you fix the x-translation and y and z rotation. you should simulate what you want.

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