# Base motion for dynamic analyses **URL:** \ **Category:** Feature Requests\ **Created:** [September 5, 2023, 7:29pm UTC](https://prepomax.discourse.group/t/base-motion-for-dynamic-analyses/1062 "2023-09-05T19:29:02Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [September 5, 2023, 7:29pm UTC](https://prepomax.discourse.group/t/base-motion-for-dynamic-analyses/1062/1 "2023-09-05T19:29:02Z")
One very useful feature that’s missing in terms of dynamic analyses is the support for base motion. It’s used to define prescribed displacement or acceleration in modal dynamics and steady state dynamics analyses. It just operates on boundary conditions defined in the frequency step preceding the modal superposition analysis. Thus, the definition is very simple (no need for references to existing BCs - they will be detected automatically): `*BASE MOTION, TYPE=DISPLACEMENT or ACCELERATION (default), DOF=1-3, AMPLITUDE=amplitude_name` Of course, it can be added using the keyword editor but it would be good to have it in GUI as one of the very few missing pieces in terms of dynamic analysis support. ---
**Author:** ![synt](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/synt/32/4658_2.png) [@synt](https://prepomax.discourse.group/u/synt)\ **Post date:** [September 6, 2023, 11:01am UTC](https://prepomax.discourse.group/t/base-motion-for-dynamic-analyses/1062/2 "2023-09-06T11:01:50Z")
thanks for considering base motion features, also it will be great feature when combined plot capabilities of PrePoMax. probably i can make small contribution to common data of earthquake base motion recorded in displacement history format, not an acceleration as provided. and giving such as tutorial or tips to convert them using another opensource software for those who interested.