1. S8-1 SECTION 8 ENFORCED MOTION

2. S8-2 ENFORCED MOTION n Used to analyze constrained structures with base input acceleration, velocity, displacement. n Common examples are drop test & shock test and earthquakes (for transient analysis) and swept-sine shaker test simulation (for frequency response analysis).

3. S8-3 ENFORCED MOTION n Patran/Marc input for automatic enforced motion defined as u displacement n The analysis could be Transient or Frequency response

4. S8-4 n First, a time dependent Load Case is created and is made current. This will ensure that all subsequent LBC forms relate to this time dependent loading. ENFORCED MOTION IN TRANSIENT ANALYSIS

5. S8-5 n A time dependent field is set up, in this case a rectangular pulse input ENFORCED MOTION IN TRANSIENT ANALYSIS (Cont.)

6. S8-6 n Now define the loading as Displacement n The direction of the displacement is defined in Spatial Dependent. n The Time Dependent is defined in the field. n The grids where the enforced motion are applied are picked in Select Application Region. ENFORCED MOTION IN TRANSIENT ANALYSIS (Cont.) Grid 1 Z direction

7. S8-7 USING “LARGE MASS” METHOD IN TRANSIENT RESPONSE n Large Mass Method to apply enforced accelerations. n In this method, apply forces {P(t)} to the structure rather than accelerations. If enforced motion is selected, it is assumed that the user is imposing the motion on a “large mass.” Therefore, the force to move the “large mass” is proportional to acceleration.

8. S8-8 USING “LARGE MASS” METHOD IN TRANSIENT RESPONSE (Cont.) n For enforced acceleration n Larger mass should be ~10 6 times the structure mass u If the Large Mass is too small then a coupling may occur between the Large Mass and structural mass. u If the Large Mass is too big, numerical conditioning problems may occur. Large Mass m Rigid Body Structure of Interest (M L = large Mass and Structural Mass, M, is not significant.) M=~10 6 m

9. S8-9 USING “LARGE MASS” METHOD IN TRANSIENT RESPONSE (Cont.) n Replace the constraints with connections to the Large Mass using an RBE2 and POINT MASS method. POINT MASS RBE2 Structure Connected to ground n It is vital that the RBE2 connections model the same DOF’s as the original constraints, otherwise the boundary conditions and hence the response, will change.

10. S8-10 n Now define the loading as Force n The direction of the force is defined in Spatial Dependent. n The Time Dependent is defined in the field. n The grids where the enforced motion are applied are picked in Select Application Region. ENFORCED MOTION IN TRANSIENT ANALYSIS (Cont.) Grid 1 Z direction