What is the difference between FMESH and MESH in MCNP?

In summary, FMESH and MESH cards in MCNP are used to define the geometry and materials of a system in a Monte Carlo simulation. FMESH cards are used for complex geometries with curved surfaces, while MESH cards are used for simpler, more regular geometries. These cards can be used together in a single simulation, with FMESH cards providing more precision but requiring more input data and longer computation times. The use of these cards can greatly impact the accuracy of the simulation, but there are some limitations to their use, such as compatibility issues and the need for additional input data. It is important to carefully consider the needs of the simulation and consult the MCNP user manual before using FMESH and MESH cards.
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19matthew89
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TL;DR Summary
Difference between MESH card and FMESH card
Hi everyone,

I am struggling to understand the difference between FMESH and MESH.
FMESH is used to create a mesh superimposed with the geometry but...what does MESH? Is it only involved in weight-window generation and not needed for mesh tallies?

Thanks in advance for the clarification.
 
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  • #2
I had a read and I'm pretty confident you are right. FMESH is a tally mesh, and MESH is a variance reduction mesh.
 
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1. What is the difference between MCNP FMESH and MESH cards?

The FMESH card in MCNP stands for "Finite Element Mesh" and it is used to define complex geometries in a more efficient way compared to the traditional MESH card. The FMESH card allows for more control over the meshing of the geometry and can handle more complex shapes.

2. When should I use FMESH instead of MESH cards?

FMESH cards are ideal for modeling complex geometries with curved surfaces or non-uniform shapes. They also provide better accuracy and efficiency for neutron transport calculations compared to MESH cards. However, for simple geometries, MESH cards may be more suitable as they are easier to define and require less computational resources.

3. Are there any limitations to using FMESH cards?

One limitation of FMESH cards is that they are only available in the newer versions of MCNP, such as MCNP6. Older versions of MCNP do not have the capability to use FMESH cards. Additionally, FMESH cards may require more memory and computational resources compared to MESH cards, which could affect the simulation time.

4. Can I use both FMESH and MESH cards in the same MCNP simulation?

Yes, it is possible to use both FMESH and MESH cards in the same simulation. However, it is important to note that the FMESH card will take precedence over the MESH card. This means that any overlapping regions defined in both cards will be meshed according to the FMESH card, and the MESH card will be ignored for those regions.

5. How do I know which card to use for my specific simulation?

The choice between using FMESH or MESH cards depends on the complexity of the geometry and the desired accuracy of the simulation. If the geometry is simple and accuracy is not a major concern, then MESH cards may be more suitable. However, for complex geometries and higher accuracy, FMESH cards should be used. It is always recommended to consult the MCNP user manual and perform sensitivity studies to determine which card is best for your specific simulation.

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