 # Elastic Support

Elastic support can be used to introduce virtual springs on selected face nodes, thus constraining the body via springs. User can manually define specific stiffness for the springs. There are two spring stiffness criteria offered in SimScale:

## 1) Isotropic spring stiffness

Using this option will assume the spring stiffness in all directions i.e. x, y and z. The figure below elaborates the case. Springs as shown in the figure above are grounded to the nodes. Therefore, in the undeformed state the moving end of the springs remain on the nodes to which they are grounded. After the application of load/displacement, the springs along that direction reacts against the applied load/displacement as shown in the above figure. One can therefore use isotropic stiffness criteria if constraining a geometry via specific spring stiffness in all directions is required.

## 2) Orthotropic spring stiffness

Using this option will assume the stiffness along a specified direction. The figure below elaborates the case. The grounding criteria for spring remains same as discussed above. The only difference is that the spring will react in only the direction where nonzero stiffness is defined. An example in the above figure shows that the body is unconstrained in y direction since zero stiffness is defined along that direction. One can therefore use orthotropic stiffness criteria if constraining a geometry via specific spring stiffness in certain direction/s is required.

Furthermore, each spring stiffness criteria has two types of stiffness definition; distributed and total. Distributed can be used if the defined stiffness needs to be distributed with respect to face area on which it is applied. Whereas, total will apply the defined stiffness value on all nodes of the face.

### Applications of elastic support

There can be several applications of elastic support. Two of the application cases are discussed below.

## 1) Constraining rigid body motion

In some of the analysis cases, a part of an assembly needs to set free in order to perform a specific behavior. If one of the part in an assembly is free to move i.e. unconstrained, then a free body motion or in other words rigid body motion will likely take place at the start of the simulation. Due to which, the solution matrix will diverge leading to a failed simulation. This case occur most of the time when one like to perform an analysis including physical contact between two parts of an assembly. If either one or both parts are kept unconstrained before the contact take place will lead to a diverge solution. In these cases, the unconstrained body can be hold by springs with a very low stiffness at the start of the simulation in order to avoid this rigid body motion behavior.

An example of elastic support use in order to avoid this behavior is shown in the figure below. The figure shows an assembly of a sheet metal stamping case. The stamping process is performed with metal sheet being unconstrained. Leaving it unconstrained will lead to free motion of the middle metal sheet at start of the simulation. Therefore, an elastic support with a reasonable value is applied on one of the sheet face (highlighted red in above figure). The virtual springs will hold the metal sheet until the stamping takes place.

Hint

Make sure that the spring stiffness is less enough so that it don’t effect the results. A high value of stiffness will result in partially constrained body along the stiffness direction. A good approximation can be the value until which the results remain independent of the spring stiffness. This will require running couple of simulations for different stiffness value e.g. 500, 1000, 5000 etc.

## 2) Replacing physical spring

Another application of elastic support is to replace a physical spring with a virtual one. By doing this one can avoid complex spring structure/s in an assembly thus saving the overall simulation setup and computation time. An example can be seen in the figure below. The figure above shows an example case of pneumatic actuator. The right figure shows that the physical spring is replaced by an elastic support applied on the red highlighted region. There are two things that can be attained in this case:

• Complex spring structure is avoided.
• Only a quarter model is considered due to symmetry after the removal of spring.