# yade-dev team mailing list archive

## [Question #692476]: Streamlined body

```New question #692476 on Yade:

How to define geometry in case of flow around a cylinder?
If you set the geometry the way I do it, then the time step becomes nan.

###
def __init__(self):
O.periodic = True
O.cell.setBox(0.4,0.4,0.4)

numspheres=1000
young = 5e6
density = 1000

O.materials.append(mat1)
mat2 = FrictMat(young=young,poisson=0.5,frictionAngle=0,density=0,label='wallmat')
O.materials.append(mat2)

epsilon = 1e-08
minval = 0 + epsilon
maxval = 0.4 - epsilon
#wall coords, use facets for wall BC:
v0 = Vector3(minval, minval, minval)
v1 = Vector3(minval,minval,maxval)
v2 = Vector3(maxval,minval,minval)
v3 = Vector3(maxval,minval,maxval)

v4 = Vector3(minval,maxval,minval)
v5 = Vector3(minval,maxval,maxval)
v6 = Vector3(maxval,maxval,minval)
v7 = Vector3(maxval, maxval, maxval)

lf0 = facet(vertices=[v0,v1,v2], material='wallmat')
O.bodies.append(lf0)
lf1 = facet(vertices=[v0,v2,v3], material='wallmat')
O.bodies.append(lf1)

uf0 = facet(vertices=[v4,v5,v6], material='wallmat')
O.bodies.append(uf0)
uf1 = facet(vertices=[v4,v6,v7], material='wallmat')
O.bodies.append(uf1)

ff0 = facet(vertices=[v1,v2,v6], material='wallmat')
O.bodies.append(ff0)
ff1 = facet(vertices=[v1,v6,v5], material='wallmat')
O.bodies.append(ff1)

bf0 = facet(vertices=[v0,v3,v7], material='wallmat')
O.bodies.append(bf0)
bf1 = facet(vertices=[v0,v7,v4], material='wallmat')
O.bodies.append(bf1)

######cylinder######
b = Body()
b.shape = cyl
b.mat = O.materials['wallmat']
O.bodies.append(b)

#spheres
mn, mx= Vector3(minval + epsilon, minval + epsilon, minval + epsilon), Vector3(-0.06, maxval - epsilon, maxval - epsilon)
sp = pack.SpherePack();
sp.makeCloud(mn,mx,rMean=0.00075,rRelFuzz=0.10, num=numspheres)