Define Objects: Bodies


Define Objects: Surfaces| Volumes| Components| Bodies| Forces

Bodies group components into logic sets; as such, bodies can be viewed as "containers" for components. In turn, components are containers for surfaces and/or volumes. The primary purpose of a body is to construct an entity which moves as a unit in a dynamic simulation. For example, the airframe component and propulsor components can be grouped into a body, since the entire aircraft must move as a unit during a maneuver.

Another potential use for bodies is to generate force/moment reports for specific sets of components. For each body specified, the solver generates a forces.Body.BodyName file which contains the summed forces and moments on all components that make up the body. The center of gravity specified for the body is the CG used to compute moments for all components in a given body. NOTE: if the hierarchy from bodies down to surfaces/volumes is traversed, a surface and/or volume may only appear once. For example, if components 1 and 2 contain surface 5, a body may not contain both components 1 and 2.

The body with an ID of 1 has a special meaning to the solver; the grid moves with this body. If no body has an ID of 1, the grid is fixed at its initial position for all time.


Generic


Container Body 		A container body simply groups components into a logical set, that may be used to report forces and moments on the set as a whole.

The format for the generic body definition is given below: 

body 1: component_list = [list_of_components]
        <motion = none>
        <xcg = (# # #)>
        <vcg = (# # #)>;
If an empty list is desired, use the keyword "none" for "list_of_components". Moments are computed about the center of gravity specified by the "xcg" parameter.

If "vcg" is nonzero for body 1, the freestream conditions are set to zero, and the grid is translated by the velocity given (this, in essence, is a relative frame simulation in a translating frame). The "vcg" parameter is ignored for all bodies except for body 1.

Example: 
body 1 [name=Plane]: 
        component_list = 1,2,4
        motion = none
        xcg = (1.2 4.3 2.1)
        vcg = (0.0 0.0 0.0);

 
 

SIXDOF


Body under control of the 6-DOF model 		The primary use for a body is to group components to place them under control of a 6-DOF model for time-dependent maneuvers. The format for the generic body definition is given below: 
body 1: component_list = [list_of_components]
        motion = sixdof
        xcg = (# # #)
        vcg = (# # #)
        ocg = (# # #)
        mass = # # #)
        Ixx = # 
        Ixy = # 
        Ixz = #
        Iyy = #
        Iyz = #
        Izz = #;

The xcg,vcg, and ocg parameters give the initial position, initial velocity, and initial rotation rates (all at time t=0), respectively. The mass and moments of inertia are suitably nondimensionalized.

Example: 
body 1 [name=Plane]: 
         component_list = 1,2,3
         motion = sixdof
         xcg = (4.3 2.1 3.2)
         vcg = (0.0 0.0 0.0)
         ocg = (0.0 0.0 0.0)
         mass = 1.2
         Ixx  = 1.0
         Ixy  = 0.0
         Ixz  = 0.01
         Iyy = 1.2
         Iyz  = -0.3
         Izz  = 1.3;

For further information related to the materials in this web site, USS_U2NCLE, U2NCLE,  SolidMesh, DIVA or information related to their use, please contact:

David L. Marcum
marcum@erc.msstate.edu

Phone: (662) 325-3193,   FAX: (662) 325-7692

Computational Simulation and Design Center
Engineering Research Center for Computational Field Simulation
Mississippi State University
Box 9627, Mississippi State, MS  39762

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