Define Objects: Volumes


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

Volumes are defined as groups of vertices in the mesh delimited by surfaces. In a dynamic grid context, volumes always move as a distinct unit. Distinct volumes may only be formed within a mesh by using gridmerge to merge two meshes into one. In the course of this operation, the nodes belonging to each constituent grid receive a unique volume ID.

For a grid which was not constructed through gridmerge, only one volume exists with an ID of one; in this case, it is not required to define a volume as long as "static" is an appropriate definition for volume one.


Static

Type: Static
Subtype: None		 A static volume has no specific movement properties; it remains fixed with respect the primary body throughout the simulation.
Example: 
volume 1 [name=Main_Volume]: static;


 
 

Rotating Volume

Type: Rotating
Subtype: None		 To specify a volume that rigidly rotates, one must give the axis of rotation and rotation rate. Note that all coordinates given must be nondimensionalized by L_ref . The nondimensional rotation rate (omega) is W_nd = W*L_ref/U_ref. The direction of rotation is right-handed around the vector defined by p1 and p2 (the vector begins at p1 and ends at p2).

Nested rotating volumes are supported by the "parent" option for this volume definition. Normally, the parent is set to zero, which indicates that the volume has no parent. If the rotating volume is nested within another rotating volume, the parent must be set to the volume ID of this other encompassing volume.

The most common use for rotating volumes is to allow for the simulation of embedded propulsors in an unstructured simulation.

Example: 
volume 2 [name=Rotating_Piece]: rotating
     p1 = (0.0 0.0 0.0)
     p2 = (0.0 0.0 1.0)
     omega = 2.0
     parent = 0;


 
 

Stepped Volume

Type: Rotating
Subtype: Stepper		 A "stepped" volume denotes a volume which is rotated into a certain position and held in this position for the duration of the simulation. Like the generic rotating volume (above), the volume is rigidly rotated about the axis specified. The direction of rotation is right-handed around the vector defined by p1 and p2 (the vector begins at p1 and ends at p2). The "degrees" parameter gives the amount, in degrees, to rotate the volume into place.

Nested rotating volumes are supported by the "parent" option for this volume definition. Normally, the parent is set to zero, which indicates that the volume has no parent. If the rotating volume is nested within another rotating volume, the parent must be set to the volume ID of this other encompassing volume.

The most common use for stepper volumes is to simulate control surfaces at certain deflections without resorting to changing the geometry specification and regenerating an entirely new grid.

Example: 
volume 2 [name=Stepped_Piece]: rotating stepper
     p1 = (0.0 0.0 0.0)
     p2 = (0.0 0.0 1.0)
     degrees = 15.0 
     parent = 0;



Oscillating Volume

Type: Rotating
Subtype: Oscillating		 An oscillating volume denotes a volume which undergoes rotational motion, but the amount of which sinusoidal function of time (rather than a linear function of time). Like the generic rotating volume (above), the volume is rigidly rotated about the axis specified. The direction of rotation is right-handed around the vector defined by p1 and p2 (the vector begins at p1 and ends at p2). The "degrees" parameter gives the maximum amount, in degrees, to rotate the volume into place. The "frequency" parameter gives the frequency of the sinusoid in Hertz, and the "phase" parameter gives the phase angle, in degrees. The angle through which the volume is rotated at a given time step is 
deg_rot = D * sin ( 2 * pi * f * t + P )
    D = max degrees to rotate, in radians
    f = frequency,in Hertz
    t = current time
    P = phase angle, in radians
Although the above formula is given in terms of radians (for clarity), the input phase angle and maximum angle of rotation should be given in degrees.

Nested rotating volumes are supported by the "parent" option for this volume definition. Normally, the parent is set to zero, which indicates that the volume has no parent. If the rotating volume is nested within another rotating volume, the parent must be set to the volume ID of this other encompassing volume.

The most common use for oscillating volumes is to simulate a control surface undergoing a specific periodic motion.

Example: 
volume 2 [name=Oscillator_Piece]: rotating oscillator
     p1 = (0.0 0.0 0.0)
     p2 = (0.0 0.0 1.0)
     degrees   = 15.0 
     frequency = 52.0 
     phase     = 30.0 
     parent = 0;



Prescribed Volume

Type: Rotating
Subtype: Prescribed		 A prescribed volume denotes a volume which undergoes rotational motion, but the amount of which is a user defined function of time. Like the generic rotating volume (above), the volume is rigidly rotated about the axis specified. The direction of rotation is right-handed around the vector defined by p1 and p2 (the vector begins at p1 and ends at p2). The format of the rotationfile is computational time in the first column and the rotation amount, in degrees, in the second column, e.g. 
 t_0 theta_0
  .     .
  .     .
  .     .
 t_n theta_n

The rotation amount at intermediate times is found by linear interpolation.

Nested rotating volumes are supported by the "parent" option for this volume definition. Normally, the parent is set to zero, which indicates that the volume has no parent. If the rotating volume is nested within another rotating volume, the parent must be set to the volume ID of this other encompassing volume.

The most common use for prescribed motion volumes is to simulate a control surface undergoing a general rotation time history. Note that the linear rotation, stepper, and oscillator volumes can all be defined using the prescribed motion.

Example: 
volume 2 [name=Prescribed_Piece]: rotating prescribed
     p1 = (0.0 0.0 0.0)
     p2 = (0.0 0.0 1.0)
     rotationfile = presribed_rotation.dat
     parent = 0;

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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