20 Feb 3D modelling applied to CFD and FEM simulations
When your intention is running a CFD (Computational fluid dynamics) or FEA/FEM (Finite element analysis/Finite element method) simulation the first task to complete is about 3D modelling. Everything starts from there: a simple CAD file which summarizes the simulation you are about to perform, a CAD file that describe somehow the prototype you want to test. Whilst most of you may already be expert in 3D modelling, it is important to note that CFD and FEM models are quite different compared with normal 3D models. Here we investigate together what are the most important simplification to obtain before running a simulation.
REMOVE USELESS PARTS FROM ASSEMBLIES
In general, 3D models are defined by an assembly file that gather together a very high number of different parts (from screws and bolts to flanges, wheels …). This characteristic is very useful when creating the BOM (Bill of Material), a list of all the separate parts that compose all together the assembly, with dimensions, materials and all their features. FEM and CFD simulations, on the other side, can neglect most of these parts, because the would have minimal or no effect on the simulation output. At the same time, keep in mind that both FEM and CFD simulations intention is the study of a single aspect of the body, so if your assembly if composed by a very high number of parts probably you are about to study a very high number of effects for which the simulation is not studied for.
SIMPLIFY ALL SECONDARY FEATURES
With the same spirit we used to remove minor parts, it is now fundamental a simplification of the single part file. Secondary features generally have small influence on the domain, whilst have huge impact on the simulation. Just think of mesh generation: we have have sharp cells and spikes which definitely affect our simulation results. It is recommendable the elimination of this aspects: small holes, sharp corners, small feature compared to the maximum geometry dimension. It is fundamental the user understand what is worth simulating and what instead can be neglected because the impact on the simulation is rather small.
More in deep: mesh quality
EXTRACT THE FLUID VOLUME FOR CFD SIMULATIONS
This aspect regards just CFD simulation. In this type of analysis, in fact, we want to study the flow behavior around our engineering shaped structure. So we need to model the fluid part of the simulation and not the solid one. This, in general, is the negative of what we are used to draw. It’s not a big problem: modern 3D modelling software have boolean operations that allows the creation of a fluid volume in a parametric way: every time you update the shape of your solid part you can automatically have an upgrade of the fluid volume. It is just a matter of using correctly assembly files and boolean functions!
More in deep: fluid volume extraction
Check also the following posts: import geometry from OnShape to CONSELF
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CFD and FEM simulation software is a very powerful tool, with its adoption optimization and innovation can be achieved in every field. To make this instrument accessible to everyone means lowering costs, but mainly to develop an infrastructure that favours a super-easy adoption by market new entrants.
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