What is the difference between FMESH and MESH in MCNP?

Thread starter 19matthew89
Start date Feb 16, 2023
Tags

Cards Mcnp Mesh

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.

Feb 16, 2023

19matthew89

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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Feb 16, 2023

Alex A

Gold Member

I had a read and I'm pretty confident you are right. FMESH is a tally mesh, and MESH is a variance reduction mesh.

FAQ: What is the difference between FMESH and MESH in MCNP?

What is the difference between FMESH and MESH in MCNP?

FMESH and MESH are both tally options in MCNP (Monte Carlo N-Particle) code used for radiation transport simulations, but they serve different purposes. FMESH is a tally that allows users to superimpose a mesh over the geometry to obtain detailed spatial distribution of results, such as flux or dose. MESH, on the other hand, is used for creating structured mesh geometries within the simulation environment.

How do FMESH and MESH affect the accuracy of a simulation?

FMESH can increase the accuracy of the simulation results by providing high-resolution spatial data, which is particularly useful for detailed analysis of radiation fields. MESH, as a geometry modeling tool, can improve the accuracy of the physical representation of complex structures within the simulation. Both contribute to the overall precision but in different aspects: FMESH in data resolution and MESH in geometric accuracy.

Can FMESH and MESH be used together in the same MCNP simulation?

Yes, FMESH and MESH can be used together in the same MCNP simulation. FMESH can be applied to any geometry, including those created using MESH. This combination allows for detailed spatial analysis over complex geometries, enhancing the capability to model and analyze intricate radiation transport scenarios.

What are the typical applications of FMESH and MESH in MCNP simulations?

FMESH is typically used in applications requiring detailed spatial distribution of radiation quantities, such as dose mapping, shielding effectiveness, and radiation therapy planning. MESH is used in applications requiring accurate modeling of complex geometries, such as reactor cores, medical devices, and intricate shielding structures. Both are essential tools in fields like medical physics, nuclear engineering, and radiation protection.

How do you define an FMESH tally and a MESH geometry in an MCNP input file?

To define an FMESH tally in an MCNP input file, you use the FMESH card followed by parameters specifying the type of tally (e.g., flux), the mesh grid dimensions, and the scoring options. For example, an FMESH tally might look like: FMESH4:n geom=xyz origin=0 0 0 imesh=10 10 10. To define a MESH geometry, you use the MESH card along with parameters that describe the structured grid, such as the number of divisions and the coordinates of the mesh points. An example MESH definition might look like: MESH 10 10 10 0 0 0 100 100 100.