ANSYS Transient- Long Piston With Cam
Long Piston with Cam
Geometry and Material:
The Geometry includes the following components: Barrel, Piston_Cam, Cam_Follower
Barrel: Rigid.
Cam: Rigid.
Cam Follower: Structural Steel.
Contacts:
Frictional contact(f=0, 0.1, 0.2) is setup in the project as shown below:
- Cam and Cam_Follower
- Cam_Follower and Barrel.-->This contact serves no purpose and can be suppressed.
Joints:
- Fixed Joint- Ground to Barrel
- Revolute Joint- Ground to Cam
- Translational Joint- Barrel to Cam Follower
Mesh:
The mesh is obtained as follows. Critical regions such as the contact between Cam_Follower and Barrel is given Face Sizing of 3mm:
Analysis Settings:
The analysis is set up for 9 steps with the following settings for all the steps.
When Stabilization is activated, it adds dampers to all the nodes. When the large displacement nodes try to move, the force is added to balance them thus favouring convergence. Energy Dissipation Ratio is given values between 0 and 1.
Boundary Conditions:
The Cam is given a Joint Rotation as shown below:
Solution:
The desired output variables are selected in the solution as shown. The File is then solved for. Since the cam and barrel are rigid, all the variables are applicable to the cam follower only.
Case comparison:
Equivalent Stress
A comparison of the equivalent stresses at friction coefficients, f=0,0.1,0.2:
The Equivalent stresses are more or less the same at different values of f. This is because the major portion of the stresses in the cam follower is mainly due to the cam and cam follower profile.
A comparison of the equivalent stresses at static and transient structural analysis:
The above graph is indicative of the fact that the inertial forces are negligible in comparision to the other forces, thus removing the necessity of a transient structural analysis.
Global Directions:
Force Reaction in the Y- Direction is due to the variations in the mating surface between the cam follower and the cam. This clear from the Joint reactions(considering only magnitude) of the Revolute joint of the Cam, Translational joint of the Cam Follower and the Fixed joint of the Barrel.
Force Reaction in the Z- Direction is also balanced similar to Y-dir.
Frictional Stress:
The Moment needed to opearte the cam is dependent on the Frictional force. The wear occuring on the cam surface is dependent on the frictional stress.
A plot of the frictional stress for f=0, 0.1, 0.2 is shown below:
Directional Displacement, Velocity and Acceleration:
The groove profile on the revolute cam surface is sinusoid, therefore, the piston motion is simple harmonic.
Based on the rotation of the joint it is easy to speculate that the angular velocity of the revolute joint is constant at 30deg per sec. The Directional Displacement, Velocity and Acceleration are expected to follow Simple Harmonic Motion Principles.
Directional Deformation:
Directional Velocity:
Directional Acceleration:
As we move to higher levels of differention (Disp --> Vel--> Acc) the noise increases. The Directional acceleration data is unreliable in this case, though it can be expected to be sinusoidal based on its SHM(simple harmonic motion) behaviour.
Inference:
The Frictional Stresses will be of main consideration in this assembly. The stresses in the cam follower in this assignment are mainly due to the analysis contraints or initial interference. As f changes, the moment needed to operate the revolute cam also increases.
The above analysis can be done in static structural as the cam follower acceleration is very small, thus a dynamic (aka transient) analysis is unnecessary with it high computing power requirements.
The Stresses in the axial direction cannot be justified as there are no constraints in the axial direction (Translational Joint). This can be due to a setup discrepancy in the analysis. Moreover, the stresses are high because the joint is rigid, but making it deformable allows for a much lower relaxed stress values.
Equivalent stress is now as low as 32MPa, compared to 1680MPa when the translational joint was rigid.