Explicit Dynamic Analysis

• Post by: Anurag Gupta
• April 25, 2022
• No Comment

Need for explicit dynamic analysis

Implicit and explicit are the two main types of time integration methods that are used to perform dynamic simulations. The explicit time integration is more efficient for the following situations-

1. To simulate the buckling and complex contact problem.

2. To model material deformation and failure at a high strain rate.

3. To model the formation and motion/propagation of shock waves.

4. To accurately simulate the short-duration high energy events.

5. To simulate the crash, impact, ballast, and drop test-related problems.

Explicit dynamics application areas

There are various application areas where explicit dynamic analysis is to be performed. Some of them are as under-

1. When the dynamic load duration is too short just like pulse load.

2. When there are extreme loadings like impact.

3. Where there is a case of failure at a material level.

4. When there exists a structural and material non-linearity.

5. When there is a case of large deformation and high strain rates.

6. When there is a buckling instability and contact-related problem.

Examples

1. Crash in the vehicle industry

2. Train car impact

3. Pressure pulse load on a block

4. Bullet impact on a plate

5. Impact loading on a RCC beam

 

Application Areas

1. Electronics applications : To quantify the failure of the components during impact and to quantify the load transfer between components.

2. Aerospace applications: To predict the failure and damage footprint when a bird strikes with the aerospace.

3. Nuclear applications: To quantify the survivability of a structure and also to quantify the energy absorption.

4. Sporting Goods applications: To study the deformation, reaction force and energy absorption mechanism.

 

Material Libraries for explicit dynamic analysis in Ansys

1. Explicit materials (include materials having time-dependent behavior)

2. General non-linear materials.

Only mass and momentum conservation are monitored in the explicit dynamic analysis.

 

Energy error warning in explicit dynamic analysis in Ansys

• It is just a warning message and this message does not means that the results are completely wrong. 
• This message stops the calculation in Explicit Dynamics and let the user examine the results before running the calculation further.
• If there is a spike in the energy history curve under solution information, then in that case we have to pay attention.
• If the trend is that the energy error is gradually increased, then in that case the results are OK. If the energy error increases very fast in a few cycles, then we have to examine the results carefully, In that case, we have to check the model setup because the problem is generally with the model setup. Other possible causes includes use of eroded elements, element size is not small enough etc.

 

End Time in explicit dynamic analysis in Ansys

The maximum length of time (starting from time zero) to be simulated by the explicit analysis refers as the end time. We should enter a reasonable estimate of it to cover the phenomena of interest. If we don’t know what end time we will kept for our model, the recommendation is that to perform a modal analysis first and then estimate T=1/f based on the first natural frequency.