COMSOL: Problem about optimization applied to a laminar flow

In summary, the conversation discusses the problem the speaker is facing with their graduation thesis, which involves a 3D stationary simulation of the brachiocephalic artery. The speaker is trying to find the optimal value for the resistance coefficient (C) using an optimization module, but the solver always returns the initial value as the optimal value, even though the resulting pressure is far from the reference pressure. The speaker has tried changing the mesh, initial value for C, and using a probe objective instead of an integral objective, but the problem persists. They ask for help and offer to provide more information or data if needed.
  • #1
tdh89
2
0
Hi all,i'm new here and i really hope that you could help me with this problem that is blocking the progression of my graduation thesis.

I'm working on a 3D stationary simulation of brachiocefalic artery; I'm using laminar flow physics with a known velocity in inlet and a normal stress in outlet. The model geometry is a simple cylinder.

For the normal stress I'm using this formula:

S=Q*C+po (where S= normal stress; Q= flow rate; po= outlet pressure (in this case venous pressure; C= resistance coefficient)

All the data are known, except the coeffcient C that is the parameter which i want to find: so I'm using the OPTIMIZATION module.

My objective is to find the C value for which the average pressure (p) in the domain is near to a reference pressure (called Pref), so i used these settings:

INTEGRAL OBJECTIVE (applied to domain):
Objective expression: abs(p-Pref)

CONTROL VARIABLE FIELD (applied to outlet boundary) :
Control variable name: C
Initial value: 0

All other are default settings.

The problem is that the solver returns always the initial value as optimal value, even if the resultant pressure is very far from the reference one.

I tried to change mesh, initial value for variable C, i used also probe objective instead of integral objective, but the problem persists: optimization solver terminate WITHOUT errors, returning back whatever initial value used for C as the optimal value.

EXAMPLE:
Pref=15000Pa (so p should be near to this value)
C initial value = 1000

Log of simulation:
Optimization Solver 1 in Solver 1 started at 28-apr-2012 19:02:53.
Optimization solver (SNOPT)
Itns Major Minor Step nPDE Error Objective
0 0 0 - 1 2.48e-011 0.3085
Number of optimization variables: 75.
Number of objective function evaluations: 3.
Number of Jacobian evaluations: 2.
Final objective function value: 0.3085111759.
Optimality conditions satisfied.
Optimization Solver 1 in Solver 1: Solution time: 110 s. (1 minute, 50 seconds)

p average on the domain= 1460 Pa ( instead of 15000!)

What's the problem?

P.S.Tell me if you need more informations or data;
 
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  • #2
i can send you a picture of the postprocessing for example.Thanks in advance for your helpJoel
 

1. What is COMSOL and how is it used in laminar flow optimization?

COMSOL is a multi-physics simulation software that allows users to solve complex engineering problems, including those related to fluid flow. It uses finite element analysis to model the behavior of laminar flow and allows for optimization of various parameters, such as geometry, boundary conditions, and material properties.

2. How does optimization improve laminar flow in engineering applications?

Optimization in laminar flow involves finding the best combination of parameters to achieve a desired outcome, such as minimizing pressure drop or maximizing heat transfer. This can lead to improved efficiency, cost savings, and overall better performance in engineering applications.

3. What are some common challenges when using COMSOL for laminar flow optimization?

Some common challenges include selecting appropriate boundary conditions, accurately modeling the geometry and material properties, and determining the most relevant parameters to optimize. It is also important to validate the simulation results with experimental data to ensure accuracy.

4. Can COMSOL be used for both steady-state and transient laminar flow optimization?

Yes, COMSOL has the capability to simulate both steady-state and transient laminar flow. Transient flow simulations are useful for studying time-dependent phenomena, while steady-state simulations provide a more simplified and efficient approach for optimization.

5. Are there any limitations or considerations when using COMSOL for laminar flow optimization?

One limitation is the assumption of laminar flow, which may not accurately represent real-world conditions in certain applications. Additionally, the accuracy of the simulation results depends on the quality of the input data and the chosen mathematical models. It is important to carefully validate and verify the results before making any critical engineering decisions based on the optimization results.

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