# Thread: Grounded joints as boundary condition for random vibe analysis in Ansys Mechanical

1. ## Grounded joints as boundary condition for random vibe analysis in Ansys Mechanical

Hello all,
I'm trying to run a random vibration analysis in Ansys Mechanical 2022 R1 of a part that is constrained to ground through Bushing Joints which are used to capture bolt stiffness. The Random Vibration boundary condition requires a single constraint input and a grounded joint is not a constraint. Is there a way to get around this problem?

In Nastran I would create my Bushing element between my part and a node with a fixed constraint, but Ansys doesn't seem to allow me to create a Bushing Joint between my part and something that I can apply a fixed boundary condition on. My workaround has been to bring in geometry that I can set as Rigid and then apply a fixed constraint to that and create Bushing body-to-body joints between the part I want to analyze and this rigid foundation part.

2. Grounded joints can be used as a boundary condition in random vibration analysis in Ansys Mechanical. Grounding a joint means that it is fixed in place and cannot move in any direction. This can be useful in situations where you want to model a structure that is connected to a rigid foundation or where you want to simulate the effect of a fixed support.

To apply grounded joints as a boundary condition, you first need to create the joint in your model. This can be done by using the "Joint" tool in Ansys Mechanical. Once you have created the joint, you can select it and set its boundary condition to "Fixed Support" or "Fixed Geometry". This will effectively ground the joint and prevent it from moving during the analysis.

When performing a random vibration analysis, you will need to specify the input loads and the frequency range of the analysis. Ansys Mechanical has several tools for generating random input loads, such as random vibration profiles and power spectral density functions. You can also specify the frequency range of the analysis using the "Frequency Response" tool in Ansys Mechanical.

After setting up the input loads and frequency range, you can run the analysis and view the results. The results will show the response of the structure to the random input loads over the specified frequency range.

3. It sounds like you are trying to run a random vibration analysis in Ansys Mechanical 2022 R1, but you are facing a challenge with the boundary condition. Specifically, you are using Bushing Joints to capture bolt stiffness, but the Random Vibration boundary condition requires a single constraint input and a grounded joint is not a constraint. One potential workaround is to use a Rigid Body constraint instead of a grounded joint. This will allow you to apply a fixed boundary condition to the Rigid Body, which can then be used as a constraint input for the Random Vibration analysis. You can create a Rigid Body by adding a new part in the model and then applying the Rigid Body constraint to it. Another workaround you mentioned is to bring in geometry that you can set as Rigid and then apply a fixed constraint to that and create Bushing body-to-body joints between the part you want to analyze and this rigid foundation part. This can also work, but it adds additional complexity to your model and may require more computational resources to analyze. In summary, using a Rigid Body constraint may be a simpler and more efficient way to address your boundary condition challenge.