13_Pendulums

There are a lot of interesting examples in the RADIOSS example, so I'll be working through them for a while.

In this post, I'll going to perform a Pendulums example.

There was also an example file in HyperMesh's installation path.

However, due to the different versions, the example in the previous post was slightly different.

In this example, we're dealing with a gravitational contact with no load, which is new to me. I was going to run the example file directly into RADIOSS and see the results, but that would take too long, so I'm going to open the rad file and study how I set it up.

 

In the guide, there are 5 pendulums, but when I open the file, there are 6 pendulums. It seems that there are many similarities and differences.

 

The left pendulum has an initial angle of 45° and follows the law of linear elasticity.

 

Linear elasticity is the ability of a material to return to its original state when subjected to small deformations. The relationship between the strain and the corresponding stress is linear, and this linear relationship is expressed by Hooke's law.

The contact between the balls is modeled using the TYPE24 contact interface.

Gravity is applied in the Z direction for all nodes, and the top of the truss is fixed in X, Y, and Z translations and Y and Z rotations.

 

That's it for the description, let's see how we applied it in HyperCrash.

 

Part

A pendulum is divided into three parts: bricks, shell, and truss, with the shell wrapped around the bricks. 
I still don't understand why the shell is wrapped around the bricks. Can't it just be a single shell element?

 

Property

Property consists of three parts: truss, shell, and brick.

truss

shell

brick

The shell's Isolid (flag for solid elements formulation) says Quadratic 16-node thick shell, full integration, variable number of Gauss points in all directions. Let's see what each of these descriptions means.

First, to understand the quadratic 16-node thick shell, you need a basic understanding of finite element method(FEM).

 

FEM is a method of calculating complex geometries by dividing them into finite elements, each of which is defined by specific points called nodes.

In FEM, the shape function is used to interpolate the physical displacement of a node from one point to another within each element, meaning that the displacement calculated at the node and the shape function can be used to calculate the displacement at another point within the element.

So the more shape functions you have (and the higher order they are), the more complicated the calculation, but the more accurate the approximation.

Thus, quadratic 16-node indicates that the displacement is approximated by 16 nodes within one element.

 

Full integration means that the number of Gauss points used to calculate stress and strain within an element is sufficient to accurately represent the strain energy of the element.

 

[q_b] In linear bulk viscosity, bulk viscotiy is a proportionality constant for stresses that occur as the volume changes in a dynamic situation such as an impact or high-speed collision, indicating that it is linearly related to the stress or strain.

 

In brick, isolid means that eight nodes are inside one element, just like in shell, which I discussed earlier.

 

A detailed explanation of the finite element method will be covered in a future post.