Coordinating Coordinate Systems in ANSYS Mechanical

Categories:

Coordinate systems are one of those things that are fundamental to Finite Element Analysis, but that most of us do not think about a lot.  They are there, but some users never fiddle with them. And some users are constantly futzing around with them.  We thought it would be a good idea to do a quick review of how they work in ANSYS Mechanical.  We will also go over the basics for  Mechanical APDL (MADL) in case you need to work with snippets.

Why Coordinate Systems Matter

ANSYS cares a lot about coordinate systems because they allow the program to solve in a standard, global, Cartesian system while allowing loads, constraints, material directions, layer information, beam sections, joints, result values, and a whole slew of other important aspects of the model to be specified in unique coordinate systems. This avoids making the user do coordinate system transformations.  At solve time, everything gets converted.

Since everyone reading this is an engineer, I’m going to assume that everyone already knows what a coordinate system is.

Coordinate Systems in DesignModeler and CAD Tools

It is important to start at the beginning.  Design Modeler and all CAD packages I’m aware of allow you to define some sort of coordinate system. Usually just Cartesian.  In workbench you can import those coordinate systems into ANSYS Mechanical by clicking “Import Coordinate Systems” from the “Advanced Geometry Options” properties for the Geometry cell in you systems.

For DesignModeler, there is an extra step.  Even if you turn on the import properties you need to dell DM which coordinate systems you want imported.  But first, be aware that there is no “coordinate system” entity in DM.  Instead it has planes, which is a coordinate system where you draw on the Z-normal plane. 

To make these available in ANSYS Mechanical, you need to scroll down to the bottom of the details for the planes you want converted over to coordinate systems, and set “Export Coordinate System” to Yes.

The following three images show setting it in DM, setting the property on the Project page, and how it shows up in Mechanical:

image  image  image

Creating Coordinate Systems in ANSYS Mechanical

In ANSYS Mechanical, coordinate systems reside in the Model Tree between Geometry and Connections.  Once you define a coordinate system it becomes available for use with any other object that can use a coordinate system.  This allows you to define it once, and then use it many times.

You always get a Global Cartesian coordinate system, called Global Coordinate System.  It is Cartesian, has an ID of 0, and sits at 0,0,0.  You can not change any of these values. Any imported coordinate systems will show up underneath the global.

To create a coordinate system you Right Mouse Button (RMB) on the Coordinate Systems branch and Insert->Coordinate System.  Or, when you click on the branch you also get a Coordinate System toolbar:

image

Click on the three color triad icon and a new system will be inserted.

Let’s look at each of the options in the details view.  But note before you go there, that the first set of group define a starting location and orientation, then you apply transformations in the last detail group in order to modify those locations.

  • Definition Group: This group specifies the type and MAPDL number for the Coordinate System
    • Type:  You can have the default Cartesian or Cylindrical here. The resulting coordinate system triads show up on your model like so.  As you can see, Z is the rotational axis, Y is tangential an X is radial.
      image   image
    • Coordinate System: In my opinion this should say Coordinate System ID because this detail lets you decide if you want ANSYS Mechanical to assign the number that MAPDL will use, or if you will.  Program Controlled is the default and is fine in most cases.  If you need to wrote a snippet to work with a coordinate system then you should change it to “Manual” and Coordinate System ID will show up.  Set it to any number over 11.

      image

  • Origin Group:  This group defines where the center of the coordinate system is.
    • Define By:  You can specify a Geometry Selection or Global Coordinates. 
      • Geometry Selection: The cool thing about using Geometry Selection is that as you update your CAD model, the origin will shift with it.  As with any geometry specification, you click on a surface, line, vertex or a collection of these.  Mechanical will calculate the geometric center of the entity of entities that you picked and place the origin at that centroid.  It will also shows the position in the global coordinate system below your geometry selection, but you can not change them.
      • Global Coordinates: Here you simply put in an X, Y, and Z value in one of two ways. The easiest is to just type them in.  Or, you click “Click to Change” for Location and pick the coordinate picker image icon and move your mouse over your model.  Mechanical calculates the point under the cursor (surface closest to camera) and displays it. When you click it will create a little blue cross on the geometry.  Choose apply on Location an it will enter that point in as the origin.  Kind of cool, if a bit inaccurate…
        image
  • Principal Axis Group: You need to tell Mechanical how to orient the coordinate system. By default it will align with the global.  But you can use Axis and Define By to specify that any of the three axis are aligned with a global axis, or with a piece of geometry.  Aligning with geometry is very useful because this is how you get coordinate systems aligned with your geometry. And when your geometry updates, that coordinate system aligns with the updated geometry.  This is especially useful when specifying a coordinate system in a cylinder because you can pick the cylinder face for your Z axis and it will move with the cylinder.
    Note that you can not specify align with Global –Z. If you want to do that you need to align with Z and use the transformation below to flip that.
    One option for “Define By” is “Fixed Vector” This uses the current orientation but disassociates it from the geometry.
  • Orientation about Principal Axis Group:  One point and a vector does not a coordinate system define. You have to specify an orientation around that principal axis.  You do that just like the how you specify that principal axis.  Define a global X, Y, or Z or a piece of geometry.
  • Direction Vectors Group:  These show the vectors for X, Y, and Z.  You can’t change them (I wish you could) and they are not a parameter. But they are useful.
  • Transformations Group:  This area allows you to stack offsets, rotations, and mirrors.
    You use the Coordinate System Toolbar to insert transformations into this group.  They are executed in order from top to bottom and the resulting orientation and position are shown in Directional Vectors and Transformed Configuration.
    There is a “Move Transform Up” and “Move Transform Down” icon as well in the toolbar to move the transformations around. There is also a delete to remove one.
    Note: When you click on a transformation in the list, the coordinate system on your model is shown AT THAT STEP, not at the final position.  This always confuses me.  So make your change, then click on the last step to see it.

Using Coordinate Systems

This is the easiest part. You simply choose one of your defined coordinate systems from a dropdown list when you create an object that is dependent on a coordinate system.  Usually this is when you can define a value based Components rather than on geometry:

 

image

Do note that you can also use coordinate systems to transform directional result values.  Simply pick the Coordinate system from the dropdown list.  This is especially important when looking at hoop or radial stresses in a cylindrical part.

Coordinate Systems in ANSYS Mechanical APDL

Coordinate systems are huge in MAPDL.  Nodes have them, elements have them, sections have them. Plus you can make a coordinate system active and every command you execute is done in that active coordinate system, and converted for you to the global. Very powerful.

If you do a search in help on “Coordinate System” you get hundreds of hits in the MAPDL manual.  Way too much to go over here.  We do recommend that you start with:

Mechanical APDL // Modeling and Meshing Guide // 3. Coordinate Systems // 3.1. Global and Local Coordinate Systems

It explains the types, the math, and the commands needed.  Read that, then move on to 3.3, 3.4, and 3.5 which talk about nodal, element and result coordinate systems.

Some key things every user should know are:

  1. All coordinate systems are defined by a number.  0-10 are reserved by MAPDL for its use.  Users can do 11 or higher.
  2. MAPDL has 6 default coordinate systems:image
    0 = Cartesian
    1 is cylindrical down the Z axis
    2 is Spherical
    4 is Cartesian, same as 0
    5 is Cylindrical down the Y axis.
    6 is Cylindrical down the X axis (not shown)
    I have no idea what happened to 3 or why 4 is the same as 0.
  3. When you change the active coordinate system with CSYS, all commands that involve coordinates get transformed into that coordinate system.  So:
    local,11,1,2.5,0,0,0,90,90
    n,1,10,10,10
    Actually makes a node at 12.5,9.8481,1.7365 in the global coordinate system.
  4. You can show local coordinate system with /psymb,csys,1

    image

  5. You can list your coordinate system definitions with CSLIST:

    image

  6. Only Cartesian and cylindrical are supported in ANSYS Mechanical, so if you need to use spherical or Toroidal you need to use snippets

Thoughts

Make sure you understand how Mechanical is using coordinate systems by bringing your models up in MAPDL.  Look at your nodes and see if they are rotated and how.  Check the coordinate systems with a CSLIST. Make sure you feel comfortable, don’t take it for granted.

Categories

Get Your Ansys Products & Support from the Engineers who Contribute to this Blog.

Technical Expertise to Enable your Addictive Manufacturing Success.

PADT Pulse Newsletter Screen Grab from March 2023

PADT’s Pulse Newsletter

Keep up to date on what is going on at PADT by subscribing to our newsletter.


By submitting this form, you are consenting to receive marketing emails from: . You can revoke your consent to receive emails at any time by using the SafeUnsubscribe® link, found at the bottom of every email. Emails are serviced by Constant Contact

Share this post:

Upcoming Events

05/24/2023

Hill Air Force Base Tech Expo

05/24/2023

Structural Updates in Ansys 2023 R1 (3) – Structural Optimization & Ex

05/23/2023

CROSSTALK 2023: Emerging Opportunities for Advanced Manufacturing Smal

05/10/2023

Signal & Power Integrity Updates in Ansys 2023 R1 - Webinar

04/26/2023

Additive Manufacturing Updates in Ansys 2023 R1 - Webinar

04/20/2023

38th Space Symposium Arizona Space Industry

More Info

04/19/2023

38th Space Symposium
Arizona Space Industry

04/19/2023

Additive Aids for Manufacturing - Webinar

04/18/2023

38th Space Symposium
Arizona Space Industry

04/17/2023

38th Space Symposium

04/13/2023

Venture Madness 2023

04/12/2023

Fluid Meshing & GPU-Solver Updates in Ansys 2023 R1 - Webinar

03/29/2023

8th Thermal and Fluids Engineering Conference

03/29/2023

Structural Updates in Ansys 2023 R1 - Composites, Fracture & MAPDL

03/28/2023

8th Thermal and Fluids Engineering Conference

03/27/2023

8th Thermal and Fluids Engineering Conference

03/26/2023

8TH Thermal and Fluids Engineering Conference

03/24/2023

Arizona BioPreneur Conference | Spring 2023

03/22/2023

2023 Arizona MedTech Conference

03/22/2023

Optimize Jigs & Fixtures with Additive - Webinar

03/15/2023

3D Design Updates in Ansys 2023 R1 - Webinar

03/08/2023

Competitive Advantages of 1D/3D Coupled Simulation - Webinar

03/01/2023

High Frequency Updates in Ansys 2023 R1 - Webinar

02/22/2023

Additive Advantages in Aerospace - Webinar

02/15/2023

Structural Updates in Ansys 2023 R1 (1) - Webinar

02/09/2023

IME 2023: MD&M | WestPack | ATX | D&M | Plastek

02/08/2023

IME 2023 MD&M | WestPack | ATX | D&M | Plastek

02/07/2023

IME 2023 MD&M | WestPack | ATX | D&M | Plastek

01/27/2023

Arizona Photonics Days, 2023

01/26/2023

Arizona Photonics Days, 2023

01/26/2023

TIPE 3D Printing | 2023

01/26/2023

Venture Cafe Phoenix Talent Night - Job Fari

01/26/2023

VFS 2023 Autonomous/Electric VTOL Symposium

01/25/2023

Arizona Photonics Days, 2023

01/25/2023

Building A.M.- Utah: Kickoff!

01/25/2023

TIPE 3D Printing | 2023

01/25/2023

VFS 2023 Autonomous/Electric VTOL Symposium

01/24/2023

VFS 2023 Autonomous/Electric VTOL Symposium

01/24/2023

TIPE 3D Printing | 2023

01/18/2023

2023 AZ Tech Council Golf Tournament

12/21/2022

Simulation Best Practices for 5G Technology - Webinar

12/14/2022

Digital Twins Updates in Ansys 2022 R2 - Webinar

12/08/2022

Tech the Halls - AZ Tech Council Holiday Mixer

12/07/2022

Electric Vehicle and Other Infrastructure Update Panel

11/30/2022

SPEOS Updates in Ansys 2022 R2 - Webinar

11/23/2022

Simulation Best Practices for Electronics Reliability - Webinar

11/16/2022

Discovery Updates in Ansys 2022 R2

11/10/2022

VentureCafe Phoenix Panel: Venture Capital in AZ

11/08/2022

2022 GOVERNOR’S CELEBRATION OF INNOVATION AWARDS + TECH SHOWCASE

11/03/2022

VentureCafe Phoenix Panel: Angel Investment in AZ

11/02/2022

High & Low Frequency Electromagnetics Updates in Ansys 2022 R2

10/26/2022

Simulation Best Practices For Chip-Package-System Design & Development

10/20/2022

Nerdtoberfest 2022

10/19/2022

2022 Southern Arizona Tech + Business Expo

10/19/2022

LS-DYNA Updates in Ansys 2022 R2 - Webinar

10/17/2022

Experience Stratasys Truck Tour - Clearfield Utah

10/14/2022

ASU School of Manufacturing Systems and Networks - Formal Opening Cele

10/14/2022

Experience Stratasys Truck Tour - Midvale Utah

10/12/2022

Experience Stratasys Truck Tour - Littleton Colorado

10/06/2022

Fluids Updates in Ansys 2022 R2 - Webinar

10/05/2022

Experience Stratasys Truck Tour - Colorado Springs

09/29/2022

White Hat Life Science Investor Conference - 2022

09/28/2022

2022 AZBio Awards

09/28/2022

Simulation Best Practices for Rotating Machinery Design & Development

09/21/2022

ExperienceIT NM 2022

09/21/2022

Additive Updates in Ansys 2022 R2 - Webinar

09/14/2022

Rocky Mountain Life Sciences Investor & Partnering Conference

09/08/2022

Ansys Optics Simulation User Group Meeting - Virtual

09/08/2022

Ansys Optics Simulation User Group Meeting

09/07/2022

SI & PI Updates in Ansys 2022 R2 - Webinar

08/31/2022

Simulation Best Practices for Developing Medical Devices - Webinar

08/24/2022

Mechanical Updates in Ansys 2022 R2 - Webinar

08/10/2022

Tucson after5 Tech Mixer: Ruda-Cardinal

08/05/2022

Flagstaff Tech Tour, 2022

08/02/2022

2022 CEO Leadership Retreat

08/01/2022

2022 CEO Leadership Retreat

07/27/2022

Thermal Integrity Updates in Ansys 2022 R1 - Webinar

07/20/2022

Simulation Best Practices for the Pharmaceutical Industry - Webinar

07/14/2022

NCMS Technology Showcase: Corpus Christi Army Depot

07/13/2022

NCMS Technology Showcase: Corpus Christi Army Depot

07/13/2022

Additive & Structural Optimization Updates in Ansys 2022 R1 - Webinar

07/07/2022

Arizona AADM Conference, 2022

06/29/2022

LS-DYNA Updates & Advancements in Ansys 2022 R1 - Webinar

06/23/2022

Simulation Best Practices for Wind Turbine Design - Webinar

06/15/2022

MAPDL Updates & Advancements in Ansys 2022 R1 - Webinar

06/01/2022

Mechanical Updates in Ansys 2022 R1 - pt. 2 Webinar

05/26/2022

Modelling liquid cryogenic rocket engines in Flownex - Webinar

05/25/2022

SMR & Advanced Reactor 2022

05/25/2022

05/24/2022

SMR & Advanced Reactor 2022

05/19/2022

RAPID + tct 2022

05/19/2022

Venture Cafe Roundtable: AI & Healthcare

05/18/2022

Tucson after5 Tech Mixer: World View

05/18/2022

RAPID + tct 2022

More Info

05/18/2022

Signal & Power Integrity Updates in Ansys 2022 R1 - Webinar

05/18/2022

Simulation World 2022

05/17/2022

RAPID + tct 2022

05/11/2022

Experience Stratasys Manufacturing Virtual Event

05/04/2022

Mechanical Meshing Updates in Ansys 2022 R1 - Webinar

Search in PADT site

Contact Us

Most of our customers receive their support over the phone or via email. Customers who are close by can also set up a face-to-face appointment with one of our engineers.

For most locations, simply contact us: