# Dynamic¶

The analysis type **Dynamic** allows the time-dependent calculation
of displacements as well as stresses and strains in one or multiple
solid bodies. In contrast to static analyses, inertia effects are taken
into account and the simulation proceeds in real time steps.

In the post-processing it is possible to analyse single time steps as well as
the dynamic performance as function of time. Similar to a *Static*
analysis you can check for undesired deformations or critical stresses and modify
your design based on those learnings.

In the following the different simulation settings you have to define are described in detail as well as the various options you can add.

## Domain¶

In order to perform an analysis a given geometrical
*domain* you have to
discretize your model by creating a mesh out
of it. Details of CAD handling and Meshing are described
in the *Pre-processing* section.

After you assigned a mesh to the simulation you can add some
optional domain-related settings and have a look on the mesh details.
Please note that if you have an assembly of multiple bodies that are
not fused together, you have to add *Contacts*
if you want to build connections between those independent parts.

## Model¶

In the *model* section everything that
defines the physics of the simulation is specified e.g. material properties,
boundary conditions etc. On the top level you can adapt some generic settings.
For this analysis type you can add a graviational load for the whole domain
and define if you want to run a geometrically linear or nonlinear analysis.

### Materials¶

In order to define the material properties of the whole domain,
you have to assign exactly one material to every part.
You can choose the material behavior
describing the constitutive law that is used for the stress-strain relation and
the density of the material. Please note that the density is used for
volumetric loads e.g. gravitation. Inertia effects are only considered in
dynamic simulations (*Dynamic*).
Please see the *Materials* section for more details.

### Initial Conditions¶

For a time dependent behaviour of a solid structure it is important to define the
*Initial Conditions* carefully, since these values determine
the solution of the analysis. In a **Dynamic** analysis the displacement, velocity and acceleration are the time
dependent variables. They define the initial state of the domain before the loads and constraints are applied.
Per default the displacements, velocities and accelerations are initialized as zero length vector.
Thus if you use the default values there will be no displacement and velocity
in the initial state. Additionally an initial stress state can be defined as it is a nonlinear analysis type.
If not changed by the user the stresses are also taken as zero initially.

### Boundary Conditions¶

In a **Dynamic** analysis you can define Constraints (Displacement boundary conditions)
and Loads (Force boundary conditions). If you want to determine
the position of a part of the domain, add at least one displacement constraint
in every coordinate direction. Otherwise it is allowed to move freely in space.
This is intended for e.g. drop tests.

In case of missing force boundary conditions (including gravitation), the geometry becomes load-free and apart from the prescribed displacement boundary conditions (constraints) no deformation will evolve. However, this might be intended to determine the strain distribution e.g. in pre-clamped structural components.

Constraint types (Displacement boundary conditions)

Load types (Force boundary conditions)

### Physical Contact¶

In the *Physical Contacts* section you
can define contact pairs of surfaces. For those faces the distance between each other
is tested during a nonlinear calculation and if they get in
touch the interaction forces that prevent those faces from interpenetrating are
taken into account. The solution method used to resolve the contact interaction
is the penalty contact method.

## Numerics¶

Under numerics you can set the equation solver of your simulation.
The choice highly influences the computational time and the required
memory size of the simulation. For a **Dynamic** analysis you can also
define the time integration scheme at this point.

## Simulation Control¶

The Simulation Control settings define the overall process of the calculation as for example the timestepping interval and the maximum time you want your simulation to run before it is automatically cancelled.

The description of the analysis type **Dynamic** refers to the use of standard dynamic analysis type using either the
**physics perspective** or the **solver perspective** choosing the **Code_Aster** solver.
You may as well choose the **Dynamic** analysis of the finite element package CalCuliX (CCX), which is only available via the
**solver perspective** (*Dynamic analysis CCX*).
See our *Third-party software section* for further information.