Element Technology

Element technology refers to the numerical formulation for the solid finite element used in the simulation. This includes the mesh order, reduced integration, and mass lumping.

The available parameters are:

• Definition: By default, Automatic is selected, allowing the solver to use the recommended default values, based on the simulation type and physical setup. By switching to Custom, the user has the option to manually select the different options, explained below.
• Mechanical or Thermal mesh order: Select between First order (linear interpolation) or Second order (parabolic interpolation) finite elements, as used for the mechanical or thermal models, respectively.
• Reduced integration: Used in second order mechanical elements, it implements a reduced number of Gauss integration points in the finite elements. The aim is to compensate for the typical over-estimation in the stiffness of the finite elements, with a side effect of slightly reducing computational time. The downside of this technique is that it can create artificial deformations related to the lower stiffness (with zero strain and no stress), also known as hour-glass modes.
• Lumped mass: For thermal elements, it allows to reduce the thermal mass to only one component, thus achieving a diagonal thermal mass matrix. This allows a faster convergence and reduction of memory consumption.

Element Definitions

It is possible to select particular reduced integration and lumped mass configurations for the different parts of the model by creating different Element definitions in the simulation tree, just below the Element technology element. Please be aware that this option is only available when using the Custom definition.

Advice on Element Technology

First-order elements are less expensive to use in terms of computational resources but require a finer mesh to properly capture the variations in the fields across the geometrical features. In thin-walled parts, we recommend the use of second-order elements. Using reduced integration second-order elements will reduce computation time, but some artificial deformations can be obtained, due to numerical errors (hour-glassing of elements).

For thermal simulations, it is always recommended to use first-order elements. This condition becomes relevant for thermomechanical simulations using second-order mechanical elements.

First-Order vs. Second-Order Elements (Structural Analysis)

In some types of structural analyses, mainly vibration analysis, second-order elements might prove to be the better choice. This is mainly because of the overly high stiffness of the first-order elements. It helps to compare a first-order element to metal sticks that do not bend easily and a second-order element to plastic sticks that you can bend in any direction that you wish. This capability of a second-order element can be visualized in Figure 2.

For vibration analysis, the result can be more accurately represented if we use a second-order element. First-order elements fail to capture this kind of deformation accurately because they use a linear shape function and can not represent the curvature of the vibrational deformation. Second-order elements, on the other hand, use a quadratic shape function and can easily represent such deformations. However, this accurate representation comes at an additional cost of computation as was previously mentioned in this article. This is mainly because other than just the corner nodes that exist in a first-order element, a second-order element also consists of mid-nodes that are part of each calculation and each calculation is trying to solve a quadratic equation instead of a linear one.

Last updated: June 27th, 2024