Why the General Joint doesnâ€™t have options for specific control of all Rotational DOFs (just like in translations) in a Rigid Dynamics model (RBD)?
March 17, 2023 at 9:00 amFAQParticipant
The general joint doesnâ€™t allow individual rotation constraint on purpose. The problem is that while constraining a single rotation among 3 sounds meaningful when considering small rotation, this is ambiguous with large rotations. See the detailed explanation below: – Joints are usually used in the context of large rotations. – When you have large rotations, the 3 rotations are not defined as rotations around the reference coordinate system of the joint but as a sequence of 3 angles. – You apply the X rotation and define a new updated intermediate coordinate system. – You apply a Y rotation around this second coordinate system and define a new update third coordinate system. – You apply a Z rotation around this last CS. – The 2nd and 3rd CS have no physics that define their position, their position is only defined by the sequence of angles. – In short, 3D rotations are not following the same math as 3D vectors, and the 3 components are not independent of each other. Now imagine that you release 2 out of 3 axis – say X and Z. – While X is clearly defined as the X rotation about the reference CS, unfortunately, as the Y rotation is not defined, the very definition of the Z rotation is ambiguous. – That’s the reason why we don’t allow combination of two free DOFS. – In the case of small rotations, the rotations around the reference CS and the rotations around the update CS are almost the same, this you could free two rotations (but it is still blocked). ** Note: As a workaround, you can work at the velocity level. -The X, Y and Z components of the joint rotational velocity are a 3D vector, they are the 3 components of the rotational velocity of the mobile CS wrt the reference CS. -Because it is a regular vector – just like displacements – you can specify any combination of zero and non zero velocities. – You can use a joint that has 3 rotations, and put a joint driver that constraints the Y rotation.
Introducing Ansys Electronics Desktop on Ansys Cloud
The Watch & Learn video article provides an overview of cloud computing from Electronics Desktop and details the product licenses and subscriptions to ANSYS Cloud Service that are...
How to Create a Reflector for a Center High-Mounted Stop Lamp (CHMSL)
This video article demonstrates how to create a reflector for a center high-mounted stop lamp. Optical Part design in Ansys SPEOS enables the design and validation of multiple...
Introducing the GEKO Turbulence Model in Ansys Fluent
The GEKO (GEneralized K-Omega) turbulence model offers a flexible, robust, general-purpose approach to RANS turbulence modeling. Introducing 2 videos: Part 1 provides background information on the model and a...
Postprocessing on Ansys EnSight
This video demonstrates exporting data from Fluent in EnSight Case Gold format, and it reviews the basic postprocessing capabilities of EnSight.
- Why is damped frequency is lower than undamped frequency with viscous damping but larger with structural damping?
- How can I change the normalization method of the vibration modes from modal analysis?
- Why does the prestress from Static analysis does not add up to the stress in Random Vibration analysis?
- A Shock absorber is represented as spring element with damping constant. Modal analysis is performed using Reduced Damped (QRDAMP) solver. How to perform a Modal super position harmonic or transient analysis further ?
- In the results of a modal analysis, how can I define that a frequency is an output parameter ?
- What does the warning “Diagonal of the mass matrix is missing in file” indicate when using RSTMAC command?
- Can you output the frequency response for a total deformation?
- What is mass moment of inertia in Point Mass used for?
- In a Modal Analysis of Mechanical, why aren’t the Participation Factors Summary under Solution Information displayed?
- If the stress is higher than ultimate strength in Response Spectrum Analysis, does this mean that the component may break or yield?
© 2023 Copyright ANSYS, Inc. All rights reserved.