One of the parameters driving the age old question of “is my mesh refined enough?” is the impact it has on the model size and the knock-on effect to runtime and computer spec. This comes into starkest relief if you have a dimensionally very large structure but where you need a fine local mesh around some detailed areas in order to refine stress intensity for e.g. fatigue life prediction.
This is the fourth article of a series concerning how to implement and use modelling methodology in CATIA V5.
In this article, we will discuss methodology and rules for sketch definition.
|Figure 1 - The skeleton geometrical set|
We will continue using the same Angle bracket example part, introduced in previous articles.
In previous articles, we have discussed the skeleton and its internal structure and organization. The subsets are numbered so that the order of the subsets coincides with the order of element insertion, thus we can work sequentially inside the skeleton.
By this point, to start our article, we will consider that we have imported all necessary external data into our part and created all the necessary reference geometry.
All these elements are to be inserted in geometrical sets:
1. Input data and 2. Reference geometry.
As visible in figure-1, sketches are to be inserted inside geometrical sets:
3. Main sketches and 4. Auxiliary sketches, both inside the Skeleton.
Attempts by the European Commission to reduce air pollution poses new challenges for engine manufacturers in the form of Stage V emissions standards. Many manufacturers can use their knowledge and experience with on-road developments to ensure off-road engine developments work efficiently.
Following on from our previously published Stage V emissions article and discussions around tougher standards for more engine types; After-treatment systems for smaller engines; and DPF in the after-treatment system, John Deere has become one of the first to release their developments.
On Cloud software is the general trend of many applications – starting with email, it has progressed through to accounting software, customer relationship software and even finite element analysis.
Almost all the solid element meshes I come across in the last decade or so have used second order 10 noded tetrahedral elements, and for most applications they are perfectly fine. There are however some applications in some FEA solvers that require a hex8 element – for example some elastomer models, magneto and electro static solvers and some acoustic solutions. How do you mesh an irregular part in hex elements?
The Design Phase
In this article, we will discuss the design stage in detail.
This is the first stage of the creation process; we will create a geometrical set called Skeleton and we will insert additional geometrical sets inside it. The component’s design intent is captured in the Skeleton geometrical set. Skeleton methodology has been around for quite some time now and the idea is to have to model’s main geometrical elements editable from one single location in the part’s specification tree. This also means that we will have many elements inserted inside this geometrical set, so for this reason we will rename them and organize them according to a specific logic.
Figure 1 - The Angle Bracket part
Specification Tree Organization
In this article, we will discuss how to organize the specification tree in a part file during the creation process.
1. Avoid cryptic specification trees
In figure 1, you can compare the difference between; a part with an organized specification tree (left side) versus a part with mixed modelling specification tree (right side). Both files present the same end geometry, considering the initial parameters specified for the design.
Figure 1 - Organised specification tree vs mixed modelling versions of Angle Bracket part
Part creation process
This is the first article of a series concerning how to implement and use modelling methodology in CATIA V5.
In this article, we will cover the creation process for a part file. We will break it down in two stages; design stage and modelling stage.
Let us imagine you need to edit a part, changing some parameters in existing features, and that the geometry update process fails after modification. Models that fail after editing are brittle and they work fine if you do not edit them!
It is for good reasons that designing laminated composite structures is sometimes known as a ‘black art’. It is not easy to intuit from the topology of and loads applied to a component what a good ply layup should be. Many companies rely on the wisdom of veteran engineers’ hard won experience, but sometimes it is necessary to take a step back and ask “what else could we try?”.
Often the design of a composite layup starts with the definition of zones within a part. The layup on each of these zones can then be fettled using FEA to arrive at a stacking sequence which can then be used to define plies.
But how do you choose the zones? Is it arbitrary based on the topology of the part? Do you just chequer-board your panel into regular squares? You could use a technique developed with MSC Nastran for one of the F1 companies.