CONGM

Concentrated Mass ElementCONGM defines a concentrated mass element at an NLFE grid.

Format

<CONGM
       id       = "integer"
       gid      = "integer"
       mass     = "real"
     [ 
       x        = "real"
       y        = "real"
       z        = "real" 
     ] 
       i11      = "real"
       i22      = "real"
       i33      = "real" 
     [ 
       i21      = "real"
       i31      = "real"
       i32      = "real" 
     ]/>

Attributes

id
Unique identification number.
gid
Grid identification number.
mass
First grid identification number.
xyz
X, Y and Z offset distance from the grid point to the center of gravity. Default for x, y and z is 0.
i11
i22
i33
Mass product of inertia about X, Y and Z axes respectively.
i21
i32
i33
Mass product of inertia about X-Y, X-Z and X-Y respectively. Default value for all three attributes is 0.

Example

The example demonstrates the definition of a CONGM element.

<CONGM id="1" gid="17" mass="10" i11="1" i22="1" i33="1"/>

Comments

  1. The x, y and z coordinates of the mass center of gravity are represented in the global coordinate system.
  2. The form of the inertia matrix about its center of gravity is calculated as:
    Figure 1.


    where, (1)
    mass = ρ d V
    and, (2)
    i 11 = ρ ( y 2 + z 2 ) d V = ρ y 2 d V + ρ z 2 d V i 22 = ρ ( x 2 + z 2 ) d V = ρ x 2 d V + ρ z 2 d V i 33 = ρ ( y 2 + x 2 ) d V = ρ y 2 d V + ρ x 2 d V i 12 = ρ x y d V i 13 = ρ x z d V i 23 = ρ y z d V
  3. All four grids defined for this element must be unique.