{"id":190032,"date":"2022-09-09T16:19:58","date_gmt":"2022-09-09T20:19:58","guid":{"rendered":"https:\/\/www.cati.com\/?p=190032"},"modified":"2022-09-09T16:21:29","modified_gmt":"2022-09-09T20:21:29","slug":"properly-requesting-reaction-forces-in-abaqus","status":"publish","type":"post","link":"https:\/\/www.cati.com\/blog\/properly-requesting-reaction-forces-in-abaqus\/","title":{"rendered":"Properly Requesting Reaction Forces in Abaqus"},"content":{"rendered":"

What are Reaction Forces?<\/h2>\n

Reaction forces are exerted by a body when an external force is being applied to it<\/a>. For instance, if you\u2019re walking on the street, there will be a resultant reaction force exerted by the street. This reaction force has two components. First, we have a vertical component to support the force from your weight. The second is a tangential component, friction. And so, from this example, it becomes apparent that those forces are only present at constrained nodes, and not free ones. This is also where Abaqus<\/a> calculates reaction forces.<\/p>\n

Let’s take a look at two ways to find and plot the reaction forces, as well as why you might choose one over the other.<\/p>\n

Model Setup<\/h2>\n

The model below shows an explicit simulation of a rigid sphere bouncing on a trampoline. We’ve modeled the trampoline bed as well as the trampoline frame using S4<\/em> elements. As for the sphere, we’re using R3D4 <\/em>elements. Lastly, we’ve modeled the springs as SPRINGA <\/em>elements.<\/p>\n

\"Set<\/p>\n

The legs of the trampoline frame are fixed in all degrees of freedom (ENCASTERED<\/em>). Additionally, the bases of all seven legs of the frame are tied to a reference point using a kinematic coupling constraint. Since this is a drop test, we’ll apply an initial velocity of 5 m\/s to the rigid sphere. A gif shows an animation of the simulation, with the color field set to von Mises<\/em> stress.<\/p>\n

\"Here's<\/p>\n

Because the legs of the frame are constrained in all degrees of freedom, Abaqus<\/a> will calculate the reaction forces there, and only there.<\/p>\n

There are two ways of extracting the reaction force:<\/p>\n

    \n
  1. To obtain the data at better resolution with a higher sampling rate, you can request the reaction force history output at the reference point tied to the legs. You can adjust the frequency to output at higher sampling rates.\n