# Waht is meaning of normal_dot_vel in IntargralBoundaryConstraint in aneurysm.py

I tried to understand the code of `aneurysm.py`. However, there is one issue which I cannot understand. What is the meaning of `"normal_dot_vel": 2.540`? The detailed code is below.

I think this code refers to the boundary condition of the outlet region and `normal_dot_vel` represents the volume flow. Is this correct? However, I cannot understand how the flow rate value of 2.540 is calculated.

If someone has knowledge of this code, please provide information. Thank you for your cooperation.

Shusaku

# Integral Continuity 1

``````integral_continuity = IntegralBoundaryConstraint(
nodes=nodes,
geometry=outlet_mesh,
outvar={"normal_dot_vel": 2.540},
batch_size=1,
integral_batch_size=cfg.batch_size.integral_continuity,
lambda_weighting={"normal_dot_vel": 0.1},
)
``````

Hi Shusaku,

yes, you are right. The `normal_dot_vel` represents the volumetric flow rate.

Volumetric flow rate is calculated with inlet area and the mean velocity at the inlet:
`vfr = inlet_area * mean_inlet_vel`

With a velocity magnitude of the parabolic velocity profile at the inlet: `inlet_vel = 1.5` you can approximate the mean velocity with: `mean_inlet_vel = 0.5 * inlet_vel`
The scaled inlet area is: `inlet_area = 21.1284 * (0.4**2)`
This results in: ` vfr = 2.54`

I hope this helps.

Best Daniel

That makes sense! I have one more question.

The variable `normal_dot_vel` has both positive and negative values. What does a negative value signify?

# Integral Continuity 1

``````integral_continuity = IntegralBoundaryConstraint(
nodes=nodes,
geometry=outlet_mesh,
outvar={"normal_dot_vel": 2.540},
batch_size=1,
integral_batch_size=cfg.batch_size.integral_continuity,
lambda_weighting={"normal_dot_vel": 0.1},
)

# Integral Continuity 2
integral_continuity = IntegralBoundaryConstraint(
nodes=nodes,
geometry=integral_mesh,
outvar={"normal_dot_vel": -2.540},
batch_size=1,
integral_batch_size=cfg.batch_size.integral_continuity,
lambda_weighting={"normal_dot_vel": 0.1},
)