24/12/2011

1

Tips and Tricks

Some Tips & Tricks in COMSOL

24/12/2011

2

Materials and settings can simultaneously be: – complex-valued

directly type in values such as 2.5-j*0.1 or exp(-j*pi/2*(z+x)) etc. for permittivity, refractive index, conductivity, or permeability

– frequency dependent

– anisotropic

– spatially varying

– nonlinear in for instance temperature T:

Ex: for conductivity, directly type in values as

5e6*(1-0.01*(T-273.15)) or

5e6*exp(-0.01*(T-273.15))

– interpolated from tabulated data

1. Express anything in terms of anything!

2. Pick the right interface!

• Example1 : Electric fields

– Electrostatics or electric currents

• Current or no currents

– Electric currents, Shell

– Magnetic field

• Current or no current

– Both Magnetic and electric

• Example 2: Fluid flow

– Stokes Flow

– Laminar

– Turbulent

• High Reynolds

• Low Reynolds

24/12/2011

3

3. Pick the right study type!

• Stationary – Steady-state solutions

• Time Dependent – Transients

• Frequency Domain – Assume solution

– Solve one frequency at a time

• Eigenfrequency – Find mode shapes and eigenfrequencies

• Frequency-Stationary, Frequency-Transient, etc. – Specialized study types for multiphysics combinations

– Treat for example an EM problem in the frequency domain and the induced heating in the time domain

– Good approximation if the heat problem is much slower than the EM problem

)sin(0 tuu

4. Expand windows!

Expand windows by double-clicking on the tab

Improved view – easier to see

Return by double-clicking again

24/12/2011

4

5. Use Functions!

Available under Global Definitions > Functions

6. Adaptive mesh

If you do not know where to refine your mesh....

...use Adaptive mesh and let COMSOL do it for you!

Available in the Study Node

Stationary problems

24/12/2011

5

7. Name your selections!

Define once – reuse any number of times

When defining materials

In physics settings

In postprocessing

...

8. Shadowing and Additive features

Physics features can be shadowing or additive

Source terms add

Constraints shadow

Improved book keeping

Avoid mixing flux contributions in one feature

Easier to control individual sources

24/12/2011

6

9. Deform your geometry!

Use to create shapes that can be described by functions

See Moving mesh ALE

You can also move and rotate things in your model

z=0.1*cos(100*Xm)*cos(100*Ym)*Zm

New in 4.2: Parameterized surfaces

• Import interpolation data for elevation

24/12/2011

7

10. Revolve your solution!

Revolve axisymmetric solution data into 3D

Only a postprocessing step

11. Plot deformations in scale!

24/12/2011

8

12. Check the Error node!

13. Visit www.comsol.com/support !

24/12/2011

9

14. Model Library Step-by-step instructions are

included for all models in the model

library – find it under the file menu

And now...

24/12/2011

10

The very most powerful trick:

15. Walk to China step by step!

-Key to solve large multiphysics models

- Start with one or a few physics

-Add more one at the time

-Simplify modeling a lot!

24/12/2011

11

Tips and Tricks