Comprehensive Fatigue Analysis Using Ansys Aqwa Hydrodynamic Diffraction Results
Introduction
Hello everyone. In this tutorial, we will conduct a diffraction analysis in ANSYS Aqwa. Follow the steps below to import and modify geometry, set up the simulation, and analyze the results.
Geometry Preparation
- Drag and drop the diffraction analysis module and import the geometry.
- Modify the geometry:
- Move it to position the reference frame at the water surface.
- Split the geometry based on the water surface.
- Place the surfaces on a new component and use the Share Topology option.
Simulation Setup
Edit the general conditions for the domain. Note that the imported geometry is free to move by default. Add a lid to the geometry. Ensure the geometry has properties of mass and inertia to obtain results about motions and forces.
For this demonstration, a coarse mesh is used. The mesh determines the maximum wave frequency allowed. In ANSYS settings, you can modify the grid area for calculations. To expedite results, ignore violations and turn off the calculation of second-order terms. By default, wave directions cover 360 degrees, but this can be modified. Select the number of frequencies in the range and solve the diffraction analysis.
Results Analysis
- Right-click on the solution to obtain:
- Hydrostatic results displayed in a table.
- Modal analysis providing information about the three vibrational modes. Animate the results to visualize each mode for better understanding.
- Use the pressure and motion plot to visually represent the body's behavior under regular waves for a given direction and frequency. Animate the results for an entire cycle and adjust direction and frequency as needed.
- Create graphs using response amplitude operators to analyze the body's motion. Identify vertical motion with maximum values for specific wave directions. Repeat for other frequency values and compare results.
- Create a 3D plot to visualize unified results for maximum and minimum values across all directions and frequencies.
Structural Analysis
- Drag and drop a module for structural analysis. Update the results in Aqwa and open ANSYS Mechanical.
- Select a suitable material with a fatigue curve and define the thickness for shell structures.
- When coupling Aqwa to Mechanical, use the Hydrodynamic Pressure tab to import data from Aqwa by selecting the outer surfaces and using the same values from the pressure and motion plot.
- View contour plots of the pressure for 180 degrees. The values for the entire cycle are available in the table.
- Create a mesh with a smaller element size than in Aqwa. Use this setup as an example. Activate large reflection if expecting plasticity and enable weak springs.
- Create a plot tracker and solve the model. During the solution, the plot tracker will display how results change for each step.
Fatigue Analysis
- Check the results. With 36 steps in total, identify the time for minimum and maximum stress values to use in fatigue analysis.
- Create a solution combination using a linear combination between the two selected times. For this demo, the coefficient is 1. Select non-proportional to calculate between the two selected times and solve the model to obtain the results.
Conclusion
This summary outlines the steps from geometry preparation in SpaceClaim to obtaining fatigue results. Be aware that the maximum value in Aqwa can be found on the table for the entire cycle in Mechanical. Thank you for watching.
Note: This tutorial is provided by Ozen Engineering, Inc.
Comprehensive Fatigue Analysis Using ANSYS Aqwa Hydrodynamic Diffraction Results Hello everyone. For the diffraction analysis in ANSYS Aqua, drag and drop this module and import the geometry. The geometry must be modified. First, move it to position the reference frame at the water surface.
Next, split the geometry based on that water surface. Then, put the surfaces on a new component and use the Share Topology option. Here you can edit the general conditions for the domain. The imported geometry is free to move by default. Here, add a lid. The new geometry is added to the geometry.
Geometry needs properties of mass and inertia so we can get results about motions and forces at the end. We can use the radius of gyration of moments of inertia. For this demo, I'm using a coarse mesh. And the mesh determines the maximum wave frequency allowed.
In ANSYS settings, you can modify the grid area for the calculations. To get results faster, we will ignore violations and turn off the calculation of second-order terms. By default, the wave directions include 360 degrees, but this can be modified. Select the number of frequencies in the range.
And now solve the diffraction analysis. Right-click on the solution to get first the hydrostatic results that are shown in this table. Next, the model analysis that provides information about the three vibrational modes. You can animate the results to see how the mode looks like.
Do it for each mode for a better understanding of your system. The pressure and motion plot provides a visual representation of what is happening with the body under the regular waves for a given direction and frequency. It is also possible to animate the results for an entire cycle.
Change the direction and frequency as desired. Create graphs to figure out the motion of the body using the response amplitude operators. Here you see the vertical motion with maximum values for specific wave directions. Repeat this for other frequency values and compare the results.
If you want to identify the maximum and minimum values for all directions and frequencies, you can create a 3D plot to visualize the unified results. Now, drag and drop a module for the structural analysis. Update the results in AQUA and open ENSYS Mechanical.
In Ansys Mechanical, select a suitable material having the fatigue curve. Then, define the thickness for shell structures as in this case. When coupling AQUA to Mechanical, the Hydrodynamic Pressure tab is available.
We must import the data from AQUA by selecting the outer surfaces and the same values that were used in the pressure and motion plot in AQUA. This is the result. Here you see the contour plots of the pressure for 180 degrees, but the values for the entire cycle are on the table.
The mesh is created with a smaller element size than in AQUA. Use this setup as an example. Activate the large reflection if you are expecting plasticity and turn on the weak springs. Create a plot tracker and now solve the model. During dissolution, the model is now in the shape of a circle.
The plot tracker will show you how the results change for each step solved. Let's check the results. We have 36 steps in total and we must identify the time for the minimum and maximum values of stress. We will use them in the fatigue analysis. To do that, create a solution combination.
We will use a linear combination between the two selected times. For this demo, this coefficient will be 1. Select non-proportional to calculate between the two selected times. And then solve the model to finally get the results. This is a summary of the steps in this model.
From the geometry in a space claim to the fatigue results. Be aware that the maximum value in AQUA can be found on the table for the entire cycle in mechanical. And that's it. Thanks for watching.
