ANSYS-Explicit Dynamics Basics Part B

Initial Conditions

By default, all bodies in an Explicit Dynamics system are at rest, unconstrained and stress free.

At least one Initial Condition, Constraint or Load must be applied to the model.

– otherwise the initial solution is the final solution and there is need to Solve.Two forms of velocity are available as Initial Conditions for Explicit Dynamics:

– Velocity (Translational)

– Angular Velocity (Rotational)

Initial Conditions

Applied to single or multiple bodies in global or local Cartesian co-ordinate systems.

– If rotational and translational velocities are applied to the same body, the initial velocity of the body will be calculated as the sum of these two conditions

Loads and Constraints

Loads and constraints that can be applied for Explicit Dynamics analyses:

– Acceleration

– Standard Earth Gravity

– Pressure

– Force

– Line Pressure

– Fixed Support

– Displacement

– Velocity

– Impedance Boundary

Acceleration

– A constant body acceleration can be applied to all bodies in the model. This results in a body acceleration vector, defined via three Cartesian components being applied to all nodes in the model prior to any constraints

Any constraints applied to the model will over-ride an applied body accelerationStandard Earth Gravity

– Special case of an Acceleration load which is applied to all bodies.

– Magnitude of acceleration is fixed at standard earth gravitational acceleration

– Acting direction can be applied in ± x, y, z directions.

Any constraints applied to the model will over-ride any applied gravity

Pressure

– Constant and tabular Pressure loads can only be applied to faces of flexible bodies.

Pressure is applied normal to element faces of scoped bodies.

Direction of applied pressure rotates with deformation of faces.

Force

– Constant and tabular Force loads can be applied to flexible and rigid bodies.

Flexible bodies

– Force loads can be scoped to points, lines and faces.

Rigid bodies

– Force loads can only be scoped to bodies.

User defines total force load applied to mesh nodes of scoped bodies.

Force applied to each node is equal to total force

divided by number of mesh nodes in the scoping.

– Resulting distribution of force is mesh dependent.

When defining tabular forces, define the analysis end time first.

Force can be applied in global or local Cartesian co-ordinate systems.

Line Pressure

– Constant and tabular Line Pressure loads can be applied to edges of flexible bodies.

Applied in a specified direction.

Does not rotate with the deformation of the model.

Fixed Support

– A Fixed Support can be scoped to flexible and rigid bodies to constrain all degrees of freedom.

Flexible bodies:

– Fixed supports can be scoped to points, lines and faces.

Rigid bodies:

– Fixed supports can only be scoped to bodies.Displacement

– Constant and tabular Displacement constraints can be applied to flexible and rigid bodies.

Flexible bodies:

– Displacements can be scoped to points, lines and faces.

Rigid bodies:

– Displacements can only be scoped to bodies.

– Displacements are ramped linearly over analysis time.

For tabular displacements, the initial value at time zero should be zero.

– For rigid bodies, the rotational degrees of freedom will automatically be constrained if a displacement object is scoped to the body.

– Displacements can be applied in global or local Cartesian co-ordinate systems.

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