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Frequency analysis of a blade

Note

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 the frequency analysis of a blade.

Import tutorial case into workspace

Step-by-Step

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’.
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  • 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.
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  • 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.
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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 “blade” 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
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The CAD model displayed in the viewer

3) Create a mesh

  • In order to create a mesh click on the “mesh geometry” button.
  • In this tutorial we simply choose Fully automatic tetrahedralization.
  • Select the parameters as shown in the figure below.
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  • Afterwards save your selection and start the meshing operation. Use the notifications panel on the lower left to check the status of the meshing process. As soon as the mesh is finished it is loaded into the viewer and you can interact with it in the same way as with the geometry before.
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Mesh creation and visualization

  • Use the operations log to get some general informations about the mesh e.g. number of nodes and elements in the mesh.

4) Specify the simulation properties

  • Switch to the Simulation Designer and add a new simulation
  • In a first step you have to choose the general simulation type. In this tutorial we want to calculate the eigenfrequencies and analyse the eigenmodes of the structure.
  • Hence we choose Frequency from the Solid mechanics selection.
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Simulation type choice

  • In the model section you can now assign a mesh to your simulation design. Choose here the previously created mesh. After you have saved your selection the mesh should be displayed in the Viewer on the right.
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  • You can choose if you want to apply a gravitational load as a preload on the whole domain in the Model section. In order to specify a gravitational load you have to determine the magnitude and the direction of the gravity field.
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  • The material is specified in the Materials section. You can add a new material by clicking on Add new material and assign a name to it. As a Frequency analysis is a linear calculation only linear elastic materials are supported. Therefore you have to determine a Young’s modulus (unit Pa = N/m²) and a Poisson’s ratio. Furthermore the density is used to enable gravitational loading. We choose the following configuration for aluminium alloy: Young’s modulus: 1.1381E11 N/m², Poisson’s ratio: 0.342, Density: 4430.0 kg/m³.
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General properties for the simulation of the crane structure

  • Use the Boundary conditions section and apply loads as preloads or prescribe displacements respectively. A new boundary condition can be added with the Add new ... boundary condition Buttons.
  • As the blade should be fixed on the one end add a new Constraint boundary condition.
  • With Fixed value one can prescribe a specific displacement, fix the boundary to zero or leave it unconstrained (not fixed). We choose fixed and zero (0) for all three directions.
  • In order to apply the boundary condition on the desired geometrical entities, we choose Pick faces (preselected) and pick one of the faces on the side of the plane. The selected face is now highlighted in red.
  • You can simply assign the boundary condition to this faces by clicking on Assign selection from viewer. Please make sure to save your selection afterwards.
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Fixed boundary condition

  • You may add a force boundary condition as preload as well. As we want to analyse the eigenmodes for a free blade we leave it with the gravitational loading as preload.
  • In the Numerics section you can choose the linear equation eigenvalue solver. Currently the only choice is the “Arpack solver”.
  • In the Simulation Control section we choose 1 core for the calculation as the eigenvalue solver is not capable of multithreading so far.
  • Here you can choose the number of calculated eigenfrequencies as well. The parameters Lower frequency limit and Higher frequency limit determine the frequency range that is checked for the eigenfrequencies.
  • If more than the previously defined maximum number of eigenfrequencies are found within these boundaries the lowest eigenfrequencies are taken for the result output.
  • If not as many eigenfrequencies as the specified number lie within the frequency range the number of calculated frequencies is reduced to these frequencies.
  • Set the values as shown in figure below.
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Simulation control properties

5) Start a simulation run

  • At last create a simulation run that holds the current configuration of your simulation and simply start your calculation by clicking on the Start button.
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  • If you select Results you can download a zipped folder containing the vtk-files of your results and use a local postprocessor on your desktop.
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6) Post-Processing

  • In order to analyse your results on the SimScale platform switch to the Post-Processor and choose your current project and run. In a Frequency run the results can be accessed by selecting Eigenfrequencies and Eigenmodes. If you select Eigenfrequencies you get an overview of the computed eigenfrequencies in a plot.
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Visualization of the calculated eigenfrequencies

  • If you want to analyse the corresponding eigenmodes switch to Eigenmodes.
  • After the post-processing environment is loaded in the Viewer, you can go through the eigenmodes by clicking on the arrows at the top of the Viewer.
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  • If you want to get a clear visual feedback of the eigenmodes the Warp by vector filter is a useful feature. Just add a new filter and choose Warp by vector. As scale factor you may choose a value around 4 as a reasonable choice. Select the displacement field for visualization.
  • Now you can clearly see the different oscillating patterns.
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Post-processing of the eigenmodes using the Warp by vector filter