Stress Simulation

This page will explain what kind of Stress simulation with Finite Element Analysis (FEA) in Msc.Visual Nastran 4D (Vn4D). The main idea in FEA are simplifying continues model become discrete that build by element and node, so simple isn’t it??

Converting continues 3D model to become discrete element are determine accuracy of the result that will be generated, so user experience and knowledge in FEA will be the main issue, big element size resulting coarse result but small element size will resulting unnecessary effort that affect in increasing computational time and hardware work load so focus on our analysis goal are the golden mean, feature in Vn4D called “Control Mesh” are the answer, where we can smoothing element size in local places which are become our analysis objective.

First we have to know what an element that generated by our software, not like CAM Software that are specializing in Finite Element Analysis such as ANSYS, there are no other option for deciding what kind of an element that use in FEA, Vn4D only using “Ten-Node Quadratic Tetrahedron” about advantage or disadvantage and why this type of element are choose by Vn4D will be discus in different post, but keep in mind that I‘m not going to guide you step by step how to perform stress simulation using Vn4D just what we get and how to achieve better result with feature in this software.

For an example I will use two different model that expose by equal force in different direction at both end, they are notched bar and hole plate which is already transform in element and node:

1. Coarse model with constant overall element size

As you see in the picture above, our 3D model become coarse especially rounded shape

2. Smoothing model with application “Control Mesh” in area that identify exposed by large stress concentration

Improvement in the critical shape area will reduce generated max error

3. Smoothing model with reducing overall element size a half from model no.1

Smoothing element size by a half contribute slightly reducing max error, continuing by reduce element size will perform better result but in contrary will increase number of element and node.

For better overview about an effect of mesh size can be seen in table below:

Model Shape

Notched bar

Hole plate

Sample No	Model 1	Model 2	Model 3	Model 1	Model 2	Model 3
Mesh size	10 mm	10 mm	5 mm	10 mm	10 mm	5 mm
Control mesh size	-	2 mm	-	-	2 mm	-
Node	581	1555	2818	1051	4979	5828
Element	276	835	1538	495	2803	3229
Max error	12.2%	6.74%	8.9%	7.2%	1.3%	3.3%

From table above we know that using “Control Mesh” feature will give significant error reduction with additional node and element that still tolerable to achieve analysis goals, but if your supported hardware are able to perform large computational process maybe I suggest to reduce overall element size since smaller element size means getting toward to continues model as our original object for stress simulation, so back again its up to you what kind of constraint do you have?