Meshing time

[TintinoB52]

Good day

I am busy with a modal analysis of a pipe. Currently I am creating the cylinder, defining the element type and material properties, setting the smart element sizing and meshing the pipe.

My problem is that any value for the smart element sizing below 9 makes the meshing process very long( going form 1sec for meshing to nearly 3min). I need to make the mesh more fine to increase the accuracy of the results but this process needs to be repeated for many different geometry setups. Is there another way of meshing my pipe?

Thank you very much for your time and help.

Here is my code. It is only setup for one geometry now as I want to first get the basic code right before adding it to a for loop:

from ansys.mapdl import core as pymapdl
import time

mapdl = pymapdl.launch_mapdl(nproc=4)
mapdl.units('SI')

def create_geometry(inner_dia,outer_dia,heigth,density,posrat,youngmod):
    mapdl.clear()
    mapdl.prep7()
    mapdl.cyl4(xcenter=0,ycenter=0,rad1=inner_dia,rad2=outer_dia,depth=heigth)
    mapdl.et(1,"SOLID187")    
    mapdl.mp('DENS',1,density)
    mapdl.mp('NUXY',1,posrat)
    mapdl.mp('EX',1,youngmod)
    mapdl.smrtsize(9)
    mapdl.vmesh('all')

    
start_time = time.time()  
    
create_geometry(inner_dia=((35.6/2)/1000), outer_dia=((38/2)/1000), heigth=0.97,density=7750,posrat=0.31,youngmod=193E9)
print('...')
geo_time = time.time()

mapdl.modal_analysis(nmode=10,freqb=10)
mod_time = time.time()
print('...')

result = mapdl.result
print(result.solution_info(2)['timfrq'])
print('...')

end_time=time.time()
tot_time = end_time-start_time
totgeo_time = geo_time-start_time
totmod_time = mod_time-geo_time

print('geometry time:',totgeo_time)
print('Modal analysis time:',totmod_time)
print('Total time:',tot_time)
mapdl.exit()

[akaszynski]

Is there another way of meshing my pipe?

You can try using a uniform mesh or control the mesh density directly using LESIZE and ESIZE.

Here's an example for manual control of mesh density:
Smoothing Element Size Transitions

Another note: you may want to run a simple convergence study by varying the mesh density, solving it, and observing when key parameters converge.

[TintinoB52]

I worked out that I was using the wrong values to define the water material. The bulk modulus for water is 2.2GPa. In theory the elastic or Youngs modulus should be 0. When input to example in workbench, correct data is being generated with possion ratio of 0.49 and Youngs modulus of 124MPa(derived from the Bulk Modulus), but with this values in apdl the results are wrong. Sorry I am deviating from the original discussion topic.

[akaszynski]

Thanks for posting the solution. If you get a chance, could you post the entire script you used? If you're ok with it, I can add it to our examples gallery to help others with similar problems.

[TintinoB52]

Hi, I will post the entire script below and you can use it, but the contact elements are not generating yet and the natural frequencies being generated for the pipe with water in, is also not correct. For the contact elements, the warning I am getting is that no elements were selected in the first place.

from ansys.mapdl import core as pymapdl
import time

mapdl = pymapdl.launch_mapdl(nproc=4)
mapdl.units('SI')


def create_geometry(inner_dia,outer_dia,heigth,density,posrat,youngmod):
    mapdl.clear()
    mapdl.prep7()
    mapdl.et(1,"SOLID186") 
    mapdl.et(2,"SOLID186")
    mapdl.mp('DENS',1,density)
    mapdl.mp('NUXY',1,posrat)
    mapdl.mp('EX',1,youngmod)
    mapdl.mp('DENS',2,998)
    mapdl.mp('NUXY',2,0.49)
    mapdl.mp('EX',2,124E6)
    mapdl.cyl4(xcenter=0,ycenter=0,rad1=inner_dia,rad2=outer_dia,depth=heigth)
    mapdl.cm('Pipe','VOLU')
    water_rad = inner_dia-(0.01/1000)
    mapdl.cyl4(xcenter=0,ycenter=0,rad1=water_rad,depth=heigth)
    mapdl.cm('Water','VOLU')
    mapdl.esize(0.008)
    mapdl.mat(2)  
    mapdl.vsweep('Water') 
    mapdl.esize(0.006)
    mapdl.mat(1)  
    mapdl.vsweep('Pipe')
    mapdl.local(1000,1)
    inner_element = water_rad - (0.02/1000)
    outer_element = inner_dia + (0.02/1000)
    mapdl.asel("S","LOC","X",inner_element,outer_element)
    mapdl.esla("S")
    mapdl.gcgen('NEW', splitkey='SPLIT', selopt='SELECT')

       
start_time = time.time()  
    
create_geometry(inner_dia=((35.6/2)/1000), outer_dia=((38/2)/1000), heigth=0.97,density=7750,posrat=0.31,youngmod=193E9)
print('...')
geo_time = time.time()
print(mapdl.mplist(mat1='all'))

#mapdl.vplot(show_lines=True,show_bounds=True,notebook=False)
mapdl.eplot(show_edges=True, show_axes=False, background='w',notebook = False)

print('...')
mapdl.modal_analysis(nmode=10,freqb=20)
mod_time = time.time()
print('...')
result = mapdl.result
print(result.solution_info(1)['timfrq'])
print('...')

end_time=time.time()
tot_time = end_time-start_time
totgeo_time = geo_time-start_time
print('geometry time:',totgeo_time)
print('Total time:',tot_time)
mapdl.exit()

[akaszynski]

Here's the updated script with contact elements generated properly. Seems that it's not affecting the solution though:

from ansys.mapdl import core as pymapdl
import time

mapdl = pymapdl.launch_mapdl(nproc=4)
# mapdl.clear()
mapdl.units('SI')


def create_geometry(inner_dia,outer_dia,heigth,density,posrat,youngmod):
    mapdl.clear()
    mapdl.prep7()
    mapdl.et(1,"SOLID186") 
    mapdl.et(2,"SOLID186")
    mapdl.mp('DENS',1,density)
    mapdl.mp('NUXY',1,posrat)
    mapdl.mp('EX',1,youngmod)
    mapdl.mp('DENS',2,998)
    mapdl.mp('NUXY',2,0.488)
    mapdl.mp('EX',2,29.2E9)
    mapdl.cyl4(xcenter=0,ycenter=0,rad1=inner_dia,rad2=outer_dia,depth=heigth)
    mapdl.cm('Pipe','VOLU')
    water_rad = inner_dia-(0.01/1000)
    mapdl.cyl4(xcenter=0,ycenter=0,rad1=water_rad,depth=heigth)
    mapdl.cm('Water','VOLU')
    mapdl.esize(0.008)
    mapdl.mat(2)  
    mapdl.vsweep('Water') 
    mapdl.esize(0.006)
    mapdl.mat(1)  
    mapdl.vsweep('Pipe')
    mapdl.local(1000,1)
    inner_element = water_rad - (0.02/1000)
    outer_element = inner_dia + (0.02/1000)
    # ...

    # generate contact elements
    mapdl.csys(1)
    mapdl.asel("S","LOC","X", inner_element, outer_element)
    mapdl.nsla("S", 1)
    mapdl.esln('S')
    mapdl.gcgen('NEW', splitkey='SPLIT', selopt='SELECT')
    mapdl.allsel()
    mapdl.csys(0)

    # for debugging... plot just the contact elements
    mapdl.esel('S', 'type', vmin=5, vmax=6)
    mapdl.eplot()
    mapdl.allsel()


start_time = time.time()  
    
create_geometry(inner_dia=((35.6/2)/1000), outer_dia=((38/2)/1000), heigth=0.97,density=7750,posrat=0.31,youngmod=193E9)
print('...')
geo_time = time.time()
print(mapdl.mplist(mat1='all'))

#mapdl.vplot(show_lines=True,show_bounds=True,notebook=False)
mapdl.eplot(show_edges=True, show_axes=False, background='w',notebook = False)


print('...')
mapdl.modal_analysis(nmode=10,freqb=20)
mod_time = time.time()
print('...')
result = mapdl.result
print(result.solution_info(1)['timfrq'])
print('...')

end_time=time.time()
tot_time = end_time-start_time
totgeo_time = geo_time-start_time
print('geometry time:',totgeo_time)
print('Total time:',tot_time)

[TintinoB52]

Thank you, I see I should have rather used csys than local. Also in the script I posted the possion ratio is 0.488 and Young's modulus is 29.9E9. I have corrected it in my comment. I will continue trying to get the script to generate correct solutions, but thank you very much for all of your help.