Static stress analysis: Underrun protection device


The content of this tutorial is not up to date with the current live version of SimScale. The tutorial setup and the results are still valid! Please do not get confused if styles like buttons and entity names have changed in the meantime.

In the following you find a step-by-step instruction for a static stress analysis of an underrun protection device. Note that the complete analysis is static, such that dynamic effects are neglected.

Import tutorial case into workspace


1) Import tutorial project

  • To start this tutorial, you have to import the tutorial project into your ‘Dashboard’ via the link above.
  • Alternatively, you can also add the tutorial project from the ‘Public Projects’ library by searching for “tutorial” name.
  • Clicking on the project, then clicking on ‘Actions’ and ‘make a copy’ option to add it to your ‘Dashboard’. This process is illustrated by the figures below.
  • Once the project is in your ‘Dashboard’, simply move the mouse over to the upper right corner click on the blue icon to open it in your workbench as shown in figure below.

2) The CAD model

  • Once the ‘Work bench’ is open you will be in the ‘Mesh creator’ tab.
  • The Mesh Creator tab is the place where you upload CAD models and create meshes for them.
  • The geometry is already available under the ‘geometry’ tree item.
  • Click on the CAD model named “underrun-protection_design-1” to load the CAD model in the viewer.
  • After a few moments, the CAD model is displayed in the viewer like shown in the figure below
  • You can interact with the CAD model as in a normal desktop application

The CAD model displayed in the viewer

3) Create a mesh

  • As Finite Element analyses are carried out on disretized domains, we have to generate a Mesh for our CAD model.
  • Therefore choose the geometry in the Navigator tree and click on the blue Mesh geometry button
  • A new tree item automatically appears in the Navigator tree under Meshes
  • SimScale has various mesh operations which allow you to specify in very detail how the mesh shall be generated.
  • When creating the new mesh, a default Mesh Operation is automatically added to your Mesh (default name is Operation 1)
  • Click on the mesh operation and select the options as shown in figure below.

The default mesh operation

  • The default mesh operation is the Fully automatic tetrahedralization which automatically adjusts its parameters based on the CAD model. This operation is a good choice for a first mesh.
  • Note that the results generated with First order elements might not be as accurate as with Second order elements. But choosing a Second order mesh will lead to longer computing times so is avoided here.
  • As for the fineness of the mesh, Coarse is sufficient. As a rule of thumb, one should make sure, that the resulting mesh does have more than one volume layer across the cross section of the model.
  • For actually starting the mesh operation hit the blue Start button on the Top of the Settings panel
  • Have a look at the Job Status box in the lower left - it always keeps you informed about the progress of your jobs

The job status box with the recently started mesh operation

  • As soon as the meshing algorithm has finished, the mesh is shown in the viewer
  • Now you can review the mesh. In this case we have quite a thin structure and a rule of thumb in meshing says, that for volume elements a mesh should always have more than one element layer over the cross section of the structure
  • Here we can see that we have three layers. So for this tutorial that is fine. However in a more detailed analysis we might want to use 2nd order elements.

The default mesh operation

  • There is also the operations log available which provides quantitative information about the mesh in terms of its node and element count and other relevant data
  • That completes the mesh generation. Let’s move on to the actual setup of the analysis.

3) Simulation setup

  • The simulation setup is done in the third tab, the Simulation Designer on the right of the Mesh Creator tab
  • The Navigator tree is completely empty - so let’s change that by clicking on the + New simulation button
  • Give it a name and confirm with Ok

Creating a new simulation in the Simulation Designer tab

  • The new simulation appears in the tree on the left
  • The first thing to do in any simulation setup is to choose on the analysis type
  • You can browse the different analysis types in the different sections and get a quick overview on the right under Analysis type description
  • In our case we are interested in running a static stress analysis, so we are going with Static under the Solid mechanics section
  • Saving the analysis type will automatically expand the tree with all the necessary items that you will have to define to run the analysis

Choosing the analysis type for the simulation: Static

  • The easiest way to set up the analysis is to work your way through the tree items from the top to the bottom
  • The green checks indicate that its item is fully specified
  • The blue dots indicate optional items
  • The red circles indicate that these items need to be specified and are not yet specified
  • The first thing to do is choose the domain on which this simulation shall be carried out. We are assigning the mesh that we just created. Do not forget to hit the Save button

Choosing the domain for this simulation: The previously created mesh

  • The next necessary tree item is the material: We are adding a new material and leave all its values as they are
  • An important step is to assign this material to our domain.
  • In our case there is only one volume available, so click on volume called volumeOnGeoVolumes_0 from the Available volumes to the Assigned volumes box
  • This means now that our domain completely consists of the steel. Imagine we would have an assembly rather than a single part - then we could assign different materials to different volumes
  • This already completes the material definition

Assigning a material to our part

  • The next red circle at the Boundary Conditions item indicates that we need to assign boundary conditions in terms of loads and constraints to fully define the simulation.
  • We start with the Constraint boundary conditions at the fixation holes
  • Every boundary condition has a type and a set of entities where the boundary condition shall be active
  • The figure shows we choose a Fixed value displacement boundary condition where we prescribe a displacement of zero in all directions
  • Next, to assign this boundary condition to the fixation holes, we select the eight holes in the mesh
  • Then we click on the blue Assign seletion from viewer button which assigns the boundary condition to these faces (they appear in the Assigned faces box)
  • Clicking on Save completes the definition of this boundary condition

First boundary condition: Fixed constraint boundary condition

  • The second boundary condition is the actual pressure load that acts on the shield of the underrun protection
  • So we add a new force boundary condition and choose Pressure as a type
  • We choose 25 bar or 2.5*10e6 Pa as the pressure value
  • And to complete the boundary condition definition, we assign the selected face via Assign selection from viewer to the boundary condition

Second boundary condition: Pressure load on one of the faces of the shield

  • The next two tree items Numerics and Simulation Control are already indicated as complete via the green checks. This means that reasonable default values are already chosen for it, so we leave them as they are.

4) Start a simulation run

  • To start a simulation on SimScale, you have to create a Run of your simulation
  • This basically means that you create a complete Snapshot of your simulation settings, that can not be changed afterwards
  • This concept makes sure that at any later point in time you can review in detail with what simulation parameters a result has been obtained
  • So we switch to the last tree item Simulation Runs and click the blue Create new run button
  • We give it a name and confirm with the Create button

Create a new simulation run

  • The new run appears in the list of all simulation runs and has the status Ready to run
  • We can check again on all the parameters of this simulation run via the Settings item of this run. This expands the whole simulation definition tree of this run. However all the item are grey, indicating that they can not be changed anymore
  • To start the simulation, we click the blue Start button of our run and confirm it.

Starting the run

  • Again, the job status box keeps us updated about the progress of our simulation
  • The status changes from Queued to Computing to Finished

The job status box with the previously started simulation run

  • Depending on the order of your mesh (2nd order will take longer than 1st order) and the amount of nodes, this simulation should take a few minutes
  • Now the results are present and we can proceed to analyze them
  • You can either download them via the blue Results dropdown menu in the run description
  • Or you switch to the integrated post-processor and post-process them online

5) Post-Processing

  • To do so, we switch to the fourth main tab Post-Processor to the right of the Simulation Designer tab
  • The Navigator tree on the left shows all runs that have been completed. In this case only the first one
  • By clicking on the Solution fields item of the run, the post-processor starts
  • Now, goto the last result frame.

The initial view of the post-processor after start

  • Now choose the solution field you are interested in, for example the von Mises stress
  • We will first have a look at the von Mises stress, so we click on it.

selecting a solution field

  • To enable the color map click on the bar icon on the right of the name ‘pressure-load’

The von Mises stress field as a color map with the scale on the right

  • The solvers on SimScale work unit independent. This means that the results are in the unit that you used in the simulation setup.
  • We completely sticked to SI units. This means that the results are as well in SI units.
  • Here one has to evaluate, depending on the material I plan to use if it is still feasible to use an elastic material model or if I switch to a plastic material model
  • Another effect can be observed: The pattern of the color map shows some mesh effects which indicates that the mesh might be too coarse or we should use 2nd order elements
  • To have a look at the displacement, we switch to the displacement field.

The color map of the displacement field

  • For the displacement units, we again get SI units. So the maximum deformation in this load case is a bit below 0.01 m
  • The online post-processor also allows to use different filters to analyze the results.
  • As an example we will use the Warp by vector filter that creates a visualization of the displacement field
  • We select the Dataset anc click on the + Add filter Button at the top
  • We choose the Warp by vector filter
  • The new filter appears in the post-processor pipeline
  • Under the filter setting we choose a scale factor. We use 20 to exaggerate the displacement field which can be helpful to get a better understanding of how a design behaves under a load
  • Confirming the filter settings with the green check brings the new visualization to the viewer

The new filtered visualization of the displacement field

  • Now you have two items in the post-processor tree: The dataset itself and the filter. You can hide each item via the eye button on the left of the item
  • When you click it you have different options how to show the item: Hide, Outline, Wireframe, Faces, Surfaces with edges or Volume
  • You can also simply download the results and read them in with your local post-processor
  • The figure below shows ParaView after the SimScale results have been imported
  • ParaView is an open source tool and you can simply download it for various platform and install it on your computer

SimScale results imported into ParaView and post-processed them locally

  • This concludes this tutorial. If you want to dive into this example more deeply, browse by in our example Public Projects library or have a look at our YouTube channel for a video tutorial on this simulation