Week 7-Long Piston With Cam

OBJECTIVE

To carry out a transient structural analysis on the provided piston and cam mechanism. Three cases of differing contact properties are to be compared via their equivalent stress, directional deformation and equivalent strain outputs.

MODEL IMAGE

PROCEDURE

1. After opening ANSYS Workbench, we are met with the Project Schematic window. Here, we can select the 'Transient Structural' analysis system on the left. Doing so creates a new project. Here, we can rename the project and also change the material if needed. We will need to right-click 'Geometry' and select 'import'. The file provided for this project should be selected. 

Once imported, we can right-click model and click 'edit'. This brings up the model in the mechanical interface.

2. In the mechanical interface, in the outline, under geometry, we can rename each of the components if needed. The material of the components should also be assigned (structural steel). In addition to that, the barrel and barrel_cam components are given the 'rigid' stiffness behaviour.

3. We then need to go to contacts under connections and flip the contacts for the interface to recognize them. In addition to that, one of the contacts involving the follower must be edited - the follower surface needs to be deselected for the contact.

Also, both contacts need to be renamed based on definition and they need to be changed to type 'frictionless'. This is case 1. Once the analysis is complete, we need to come back here after saving case 1 and change the type to frictional, then assign a frictional coefficient of 0.1 (case 2) and then 0.2 (case 3).

4. We now need to assign joints for various mechanisms in this assembly. To do that, we can right-click connections > insert > joint. We will be creating 3 joint entities. The first one is a fixed body-ground joint on the barrel surface as shown.

Next, we need to create a revolute body-ground joint situated on one end of the cam component as shown:

And finally, a translational body-body joint with the inner cylinder of the barrel as the mobile scope and the outer surface of the barrel as the reference scope:

5. Now we can define the mesh. To provide better results on the follower and groove regions, we can selectively refine the mesh in those regions using the 'sizing' option (right-click Mesh in outline > insert > sizing). The sizing size would be 3mm.

Adaptive sizing is also turned off in the general mesh settings.

6. Next, we shall work on the analysis settings. The number of steps would be 9. Selecting the first step, we can assign the following attributes:

Similarly, selecting steps 2-9, we can assign the following attributes:

7. Next, we need to right-click Transient > Insert > Joint Load. This is for the revolute joint we created earlier. The type would be rotation and we can assign tabular values as shown:

8. Now we can generate the outputs. To do this, we can right-click Solution > Insert > Strain > Equivalent (Von-Mises) (for equivalent strain) and right-click Solution > Insert > Stress > Equivalent (Von-Mises) (for stress) and right-click Solution > Insert > Deformation > Directional (X Axis).

Now, all we need to do is right-click solution again and click 'Evaluate all results'. It must be reiterated that after reaching the solution, we should save the model and go back to the contacts and change the contact type to frictional and assign the specified frictional coefficient.

After that, we will need to evaluate the results again and save it as a separate file.

Finally, when the analysis is done, we can view the results by simply clicking each of these solution entities we created, in the Outline menu.

OUTPUTS

CASE 1 - FRICTIONLESS CONTACTS

EQUIVALENT STRESS

Maximum and Minimum Stress generated

EQUIVALENT STRAIN

Maximum and Minimum Strain generated

DIRECTIONAL DEFORMATION

Maximum and Minimum Deformation generated

CASE 2 - FRICTIONAL CONTACTS WITH FRICTIONAL COEFFICIENT 0.1

EQUIVALENT STRESS

Maximum and Minimum Stress generated

EQUIVALENT STRAIN

Maximum and Minimum Strain generated

DIRECTIONAL DEFORMATION

Maximum and Minimum Deformation generated

CASE 3 - FRICTIONAL CONTACTS WITH FRICTIONAL COEFFICIENT 0.2

EQUIVALENT STRESS

Maximum and Minimum Stress generated

EQUIVALENT STRAIN

Maximum and Minimum Strain generated

DIRECTIONAL DEFORMATION

Maximum and Minimum Deformation generated

OBSERVATIONS

The frictional coefficient is increased with each case, and that explains the results. With increasing friction, the force required to overcome said friction increases, and this increases the stresses generated within the follower. This is why case 3 has the highest stresses and case 1 the lowest. This also explains the strains generated.

With the increasing stresses, the deformation created also increases. This explains the higher deformation in cases where the frictional coefficient was higher.

RESULT

The transient structural analysis was carried out on the given piston and cam model. The analyses of 3 cases with differing frictional coefficients were compared and it was established that the higher the coefficient, the higher the values generated via the outputs.