## Engineering

What is Explicit Dynamics?

Many transient dynamic simulations require extremely small integration time steps, for examples, high speed impact, drop test, or highly nonlinear problems. In such cases, the time steps may be as small as several nanoseconds, and the use of transient structural analysis system becomes impractical, since the run time would be too enormous to be accepted. The integration method used in the transient structural analysis system is called an implicit method.

The Explicit Dynamics analysis system also deals with transient structural dynamics. It uses an explicit integration method. The Explicit method is very efficient for each time step. It thus allows a huge number of time steps to be calculated with in an acceptable time. The disadvantage of the explicit method is that the integration time steps must be very small (typically microseconds to nanoseconds) to achieve a stable solution. If the dynamic behavior must be observed with in a long duration (say, several seconds), then millions or billions of time steps is required to complete the simulation. The runtime becomes impractical, unless supercomputing facilities are used.

What can be done by using Explicit Dynamics?

Explicit Dynamics is used to perform high-speed impact simulation i.e. collision of two objects. It is also used to perform drop test simulation i.e. An object falls down from a certain height onto floor.

Ansys Methodology to perform Explicit Dynamics Simulation.

A time integration method used in Explicit Dynamics analysis system. It is so named because the method calculates the response at current time using explicit information.

Once the body is meshed properly, the next step is to define initial conditions or boundary conditions. At least one initial condition is required to complete the set up.

After defining the initial conditions (initial velocity, Angular velocity), analysis setting has to be maintained as per the problem requirement. In analysis setting, time steps has to be defined explicitly. The solution time is depends on the time steps.

The time steps include:-

• Initial time step
• Minimum time steps
• Maximum time step
• Time step safety factor

In case of drop test the standard earth gravity is also taken into account.

Example:- A case study of drop test of a mobile phone is done using Ansys Explicit Dynamics. In this case a mobile phone is assumed to be fall on a concrete floor. The mobile phone is made up of Aluminum Alloy

1. Meshed Model:

2. Boundary Conditions:

. Results:

Total Deformation:

Equivalent Stress: