Pressure Cylinder Solution 14 Before applying the loads to the pressure vessel, a new analysis needs to be initial-ized. Select: Solution Analysis Type New Analysis For the type of analysis select Static. Ok The next step is to apply the loads and con-straints. The vessel will have constraints placed on areas and have a pressure applied.
- Reduction of Stresses in Cylindrical Pressure Vessels Using Finite Element Analysis 387 the nodal x, y, and z directions. In addition, symmetric boundary condition was used; hence, half of the cylindrical shell and quarter of heads model were used for the analysis.
- ANSYS Case Study: Axisymmetric Analysis of A Pressure Vessel The pressure vessel shown below is made of cast iron (E = 14.5 Msi, ν = 0.21) and contains an internal pressure of p = 1700 psi. The cylindrical vessel has an inner diameter of 8 in with hemispherical end caps. The end caps have a wall thickness of.
Step 2: Define Element Type
In the Main Menu select Preprocessor > Element Type > Add/Edit/Delete
Click on Add in the dialog box that appears:
Select Solid in the left hand menu and Quad 8 node 183 in the right hand menu and then click OK
This defines element type 1 as a 2D quadratic 8-node quadrilateral element (i.e. a rectangle with curved edges)
- Now we must define how this element behaves. Click on Options in the Element Types dialog box:
In the element type options dialog box that appears, make sure that the Element behavior is set to 'Axisymmetric' as shown in the figure below:
- Click on OK and then click close to close the Element Type dialog box.
Step 3: Define the Material Model
In the Main Menu click on Preprocessor > Material Props > Material Models, the Define Material Model Behaviour dialog box will now appear.
Expand the options in the right hand pane of the dialog box: Structural > Linear > Isotropic
In the dialog box that pops up, enter suitable material parameters for steel ( E = 207 x 109 Pa, Poissons ratio = 0.27):
Click on Ok to close the dialog box in which you entered the material parameters.
Close the Define Material Model Behaviour dialog box by clicking on the X in the upper right corner.
Step 5: Create the Model Geometry
- In the Main Menu click on Preprocessor > Modelling > Create > Areas > Rectangle > By 2 Corners
Enter the values shown below to create the bottom rectangle of the pressure vessel:
Repeat the above process and enter these values to create the side wall of the pressure vessel:
Finally, repeat the process again to create the top rectangle of the pressure vessel:
- Your screen should now look like this:
- Note: if the background of your screen is black then that is not a problem. In the image above reverse video has been used. If you want to use reverse video (i.e. have a white background) then simply go to: Utility Menu > PlotCtrls > Style > Colors > Reverse Video
Now we must add the three areas together to form one area that defines the pressure vessel geometry. Main Menu > Modelling > Operate > Booleans > Add > Areas
- Click on 'Pick All' in the picker dialog box:
- You should notice that all the areas merged into one area.
Step 6: Mesh the Geometry
- In the Main Menu click on Preprocessor > Meshing > Mesh Tool
This will open the Mesh Tool window.
- We are now going to use the Mesh Tool to set the size of the elements to all be a constant size before we begin the meshing process. In the Mesh Tool click on Areas > Set as shown in the figure below:
Use your mouse to click on the plate geometry. Once you have clicked on it, the Element Size at Picked Areas dialog box will appear. Enter 0.002 m for the Element Edge Length to define the size of each element, as shown below:
Click on OK to close the dialog box.
- In the MeshTool make sure that Quad and Free are selected and then click on Mesh. Click on the geometry in order to mesh it.
Your model should now look like this:
Step 7: Apply the Boundary Conditions
Although the solver already knows that we are performing an axisymmetric analysis due to an axisymmetric element being used, we still need to place a symmetry constraint on the edges of the model that touch the Y-axis.
Preprocessor > Loads > Define Loads > Apply > Structural > Displacement > Symmetry B.C. > On Lines pick the lines on the axis of symmetry (i.e. the two vertical lines on the left hand edge of the model) then click OK in the picker dialog box.
You should notice small 'S' symbols appear near the lines to indicate that a symmetry boundary condition has been applied.
- In order to prevent any unwanted movement of the entire model in the vertical direction (rigid body motion) we must constrain at least one node in the vertical direction:
Preprocessor > Loads > Define Loads > Apply > Structural > Displacement > On Nodes
- Click on any node in the centre of the side wall of the vessel and then click on OK
In the dialog box that appears make sure the DOFs to be constrained is set to UY only and then click on OK.
You will probably get a warning saying that 'Both solid model and finite element boundary conditions have been applied to this model. As solid loads are transferred to the nodes or elements, they can overwrite directly applied loads'. This is OK just click on Close to dismiss this dialog.
Step 8: Apply the Internal Pressure Load
- In the Main Menu click on Preprocessor > Loads > Define Loads > Apply > Structural > Pressure > On Lines
Click on all the lines representing the internal wall of the pressure vessel and then click on OK in the picker dialog box.
- The 'Apply Pres on a Line' dialog box will now appear. Enter 10000 as the pressure value as shown below:
Click on OK to close the dialog box.
- You should notice a red arrows appearing on your model to indicate the pressure load as shown below:
Step 9: Solve the Problem
In the Main Menu select Solution > Analysis Type > New Analysis
Make sure that Static is selected in the dialog box that pops up and then click on OK to dismiss the dialog.
Select Solution > Solve > Current LS to solve the problem
A new window and a dialog box will pop up. Take a quick look at the infromation in the window ( /STATUS Command) before closing it.
Click on OK in the dialog box to solve the problem.
Once the problem has been solved you will get a message to say that the solution is done, close this window when you are ready.
Step 10: Examine the Results
In the Main Menu select General Postproc > Plot Results > Deformed Shape
- Select Def + undef edge in order to show both the deformed and undeformed shapes.
Your screen should look something like this:
- It is clear that the side wall of the pressure vessel has slightly 'bowed' out due to the internal pressure. The end caps have significantly deformed in comparison to the side wall. The maximum displacement is, however, approximately 2 x 10-6 m which is well below the yield stress for steel - meaning our assumption of a linear elastic material is valid. Note that ANSYS, by default, will exaggerate any deformation by scaling it up in order to make it obvious.
Now let's examine the principal stresses: General Postproc > Plot Results > Contour Plot > Nodal Solu > Stress > 1st Principal Stress, click on OK to display the plot, which should look like this:
- The first principal stress is the Hoop Stress and we are expecting a value of approximately 55,000 Pa based on our analytical calculations. Clearly something is wrong with this plot. We are seeing very large stress concentrations at the sharp corner where the end caps join the side wall. It is likely that the stress in the side wall itself is quite close to the predicted analytical value. Let's investigate this by only displaying results for the elements at the middle of the vessel side wall:
- Utility Menu > Select > Entities
- In the 'Select Entities' dialog box that appears make sure that 'Elements' is selected in the top box and then click on OK
- The 'Select Elements' picker dialog box will appear. Change the picking type to 'Box' as shown below
- Now draw a box around the central elements in the side wall, as shown below:
- Click on OK in the 'Select Elements' picker dialog to select all the elements inside the box.
Now, only the selected elements will be displayed in any stress contour plots and the rest of the model will be ignored.
- Your screen should now look something like this:
- Now, let's replot the 1st principal stress: General Postproc > Plot Results > Contour Plot > Nodal Solu > Stress > 1st Principal Stress, click on OK to display the plot, which should look like this:
Notice that the maximum value is 56,680 Pa which is reasonably close to our predicted value of 55,455 Pa
- Let's check the Axial Stress: General Postproc > Plot Results > Contour Plot > Nodal Solu > Stress > 2nd Principal Stress, click on OK to display the plot, which should look like this:
Notice that the axial stress varies between 22,158 Pa and 23,340 Pa - which is, again, reasonably close to our predicted value of 22,727 Pa.
- Let's now check the radial stress: General Postproc > Plot Results > Contour Plot > Nodal Solu > Stress > 3rd Principal Stress, click on OK to display the plot, which should look like this:
In this case the maximum radial stress is -9,993 Pa which is very close to our predicted value of 10,000 Pa.
When you are finished looking at the results for this subset of elements, you can re-select the entire model by issuing the command: Utility Menu > Select > Everything. Now if you replot a stress contour you will see the entire model again.
Ansys Pressure Vessel Pdf Merge Free
Ansys Book Pdf
This tutorial has given you the following skills:
- The ability to model axisymmetric problems in ANSYS.
- The ability to select a subset of a finite element model and only examine the result for that subset.
- Experience in comparing the results obtained from your finite element model with other results and validating your results against the other results.
Log Files / Input Files
Click here for the log file
The log file for this tutorial may also be used as an input file to automatically run the analysis in ANSYS. In order to use this file as an input file save it to your working directory and then select Utility Menu > File > Read input from... and select the file. You should notice ANSYS automatically building the finite element model and issuing all the commands detailed above.
Quitting ANSYS
To quit ANSYS select Utility Menu > File > Exit.... In the dialog box that appears click on Save Everything (assuming that you want to) and then click on Ok