Encyclopaedia Index

2.16 Setting-up the MOFOR attributes of moving objects via In-Form.

In this chapter, the In-Form capabilities demonstrated for assigning the geometrical and kinematical attributes of moving bodies, interaction of which with the flow is simulated by MOFOR techniques.

Usually the MOFOR attributes are described in MOF data file. However the structure of MOF data file is complex and requires the specification of coordinates of a moving body position inside domain in each time step of which should be calculated by user earlier and are recorded in MOF file in the order appropriate to it format.

Use of In-Form for MOFOR purposes permits to avoid precomputations of a moving body position and does not require availability of a MOF file.

In-Form can calculate coordinates of a moving body position by the formula specified in "(MOVOB" In-Form statements which uses POS and OFFSET special functions. "(MOVOB" statement has next format


 (MOVOB of VR_OBJ_NAME is SPESIAL_FUNCTION() with PARENT=PARENT_NAME)

where VR_OBJ_NAME is a name of VR object name which is connected to a appropriate object-related coordinate system for which the current attributes are set.

The spesial In-Form flag "!PARENT=PARENT_NAME" set the name of parent object-related coordinate systems.

The OFFSET function describes the hierarchy part of the attribute settings. OFFSET is In-Form special function of declaring the frames of reference of object-related coordinate systems. Each new OFFSET function declares a new frame coordinate system and describes its position relative to its parent system. OFFSET has next format


 OFFSET(Xorigin, Yorigin, Zorigin)

where Xorigin, Yorigin, Zorigin are formulas for calculation of coordinates of the origin position of the rotation axis relative to its parent.

The POS is In-Form special function which describes the coordinates of position of moving object in appropriate object-related coordinate system. POS has next format


 POS(Xpos, Ypos, Zpos, Xang, Yang, Zang)

where

Xpos, Ypos, Zpos are formulas for calculation of X, Y, Z coordinates of the position of moving VR object in meters.

Xang, Yang, Zang are formulas for setting the rotation angle of moving VR object about X, Y, Z axis in degrees.

Each formula can contain the TIM variable which is current time in seconds at the current time step.

Probably hereafter the new special In-Form functions will be created in addition:


 VEL(Xvel, Yvel, Zvel, Xrot, Yrot, Zrot)

where

Xvel , Yvel, Zvel are formulas for setting the X, Y, Z linear velocity components of moving VR object, m/s;

Xrot, Yrot, Zrot are formulas for setting the rotation velocities of moving VR object about X, Y, Z axis, 1/s.


 ACC(Xacc, Yacc, Zacc, Xracc, Yracc, Zracc)

where

Xacc, Yacc, Zacc are formulas for setting the acceleration of linear motion of moving VR object in X, Y, Z directions, m/s^2; Xracc, Yracc, Zracc are formulas for setting the acceleration of rotation motion of moving VR object about X, Y, Z axis, 1/s^2.

The examples of In-Form use for MOFOR attributes settings are submitted below.

  • Elementary motion: linear movement

    The task is to provide the attributes for a simple motion of a 2D rectangular object called "BLOCK" with uniform velocity of 3m/s in Z-direction of computational domain starting from a given initial, stationary position of the object.

    The description the hierarchy part is not mandatory as there is only one moving object. Therefore it is enough to define the Z position of moving object in each time step.

    
     (MOVOB of BLOCK is POS(0, 0, 3*TIM, 0, 0, 0))
    

    The movement is along Z-axis. The initial position and the sizes of the BLOCK are specified in the Q1 file. Z coordinates of moving BLOCK object are described as

    Z velocity component[m/s] * current time[s].

  • Composite movement: rolling block

    The case exemplifies the specification of the attributes for composite movement: the translation of rotating block. It results in the effect of the rolling 2D rectangular object with the longitudinal (X-direction) velocity component of 0.5 m/s and the angular rotation about block centre line (Z-axis) of 30 degrees per seconds. The movement starts from the initially steady position defined in the Q1 file.

    The hierarchy part is described as follows:

    
     (MOVOB of CHAM is OFFSET(0&0&0))
     (MOVOB of BLOCK is OFFSET(0.55&0.9&0) with PARENT=CHAM)
    

    The OFFSET defines the position of the rotation axis relative to the root frame: it places the Z-axis in the middle of BLOCK initial position.

    The movement is along X-axis and the rotation about Z-axis. X coordinates of moving BLOCK object and rotation angles are described as

    
     (MOVOB of BLOCK is POS(0.5*tim&0&0&0&0&-30*tim))
    

  • Independent motions: crossing paths

    The case exemplifies the setting-up the attributes for the independent movements of two objects following their own linear trajectories in 2D, X-Y, computational space.

    The movement of the first object, called SPHERE1, starts from its stationary position at the west-south corner and follows a prescribed parabolic trajectory. The velocity of SPHERE1 is 10 m/s and is defined by interaction of gravitation force.

    The second object, SPHERE2, starts at east-south corner of the domain and follows the linear trajectory crossing the one from right to left. It has the constant velocity component of -10 m/s in X-direction and 3 m/s in Y-direction.

    The movement starts from the initially steady position defined in the Q1 file.

    The description the hierarchy part is not mandatory as two moving objects move inside one root coordinates system. Therefore it is enough only to define the position of moving objects in each time step.

    The movement of SPHERE1 object is along diagonal of XY plane. X and Y coordinates of moving object are described as

    
     vel=10.; gravt=9.81
     (MOVOB of SPHERE1 is POS(tim*:vel:&tim*:vel:-0.5*:gravt:*tim^2&0&0&0&0))
    

    The movement of SPHERE2 object is along X-axis from right to left. X coordinates of moving object are described as

    
     (MOVOB of SPHERE2 is POS(-tim*:vel:&0&0&0&0&0))
    

  • Connected objects: falling of a cracked wall

    The case exemplifies the setting-up the attributes for the connected movements of two objects following their relative rotation in 2D, Y-Z, computational space.

    The movement of the first object, called BLOCK, starts from its stationary position as a vertical wall with its base placed next to the middle of the bottom domain boundary. BLOCK is allowed to fall. It does so by rotating clockwise about X-axis of its south-high corner. The angular velocity of the fall is 75 degrees per second.

    Initially, the second smaller object, TIP, sits stationary on the top of BLOCK and can be regarded as a part of the wall. Once the whole wall starts to fall, it cracks and TIP begins to move in opposite direction by rotating counterclockwise about X- axis of the north-low corner of the BLOCK. The angular velocity of the TIP relative to the BLOCK is 180 degree per second.

    The hierarchy part is described as follows:

    
     (MOVOB of BLOCK is OFFSET(0&0&2.1))
    
     (MOVOB of TIP is OFFSET(0&2.5&-0.5) with PARENT=BLOCK)
    

    Two frames are defined: BLOCK is a parent joint, and TIP is the BLOCK's child.

    The OFFSET of BLOCK defines the position of the rotation axis relative to the root frame: it places the origin of parent related coordinate frame at the south-high corner of BLOCK initial position.

    The OFFSET of TIP defines the position of the rotation axis relative to the BLOCK frame: it places the origin of its coordinate frame at the north-low corner of BLOCK initial position.

    The movement of BLOCK object is a rotation clockwise about X plane. Rotation angle is described as

    
     (MOVOB of BLOCK is POS(0&0&0&75*tim&0&0))
    

    The movement of SPHERE2 object is a rotation counterclockwise about X plane. X coordinates of moving object are described as

    
     (MOVOB of TIP is POS(0&0&0&-180*tim&0&0))
    

  • Agitated reactor

    Impellers are the units one most commonly associates with stirred reactors. The particular design considered here consists of the ROD, mounted on rotating vertical SHAFT. The rod carries two PADDLEs, which agitate the flow. As the impeller rotates it forces the surrounding fluid to rotate with it. The design with rotating paddles is used when "in-depth" mixing is a must.

    The task of the exercise is to provide the attributes for connected movements of SHAFT-ROD-PADDLEs assembly following their relative rotation in 3D computational space. The angular velocity of the shaft is 60rpm.

    The hierarchy part is described as follows:

    
     (MOVOB of CHAM is OFFSET(0&0&0))
     
     (MOVOB of SHAFT is OFFSET(0.15&0.25&0.25) with PARENT=CHAM)
     
     (MOVOB of ROD is OFFSET(0&0&0) with PARENT=SHAFT)
    
     (MOVOB of PADDLE1 is OFFSET(0&0&0) with PARENT=ROD)
    
     (MOVOB of PADDLE2 is OFFSET(0&0&0) with PARENT=PADDLE1)
    

    Four frames are defined: SHAFT is a parent joint, and ROD, PADDLE1 and PADDLE2 are the SHAFT's children.

    The OFFSET of SHAFT defines the position of the rotation axis relative to the ROOT frame: it places the origin of parent related coordinate frame at the middle of the SHAFT bottom face of its initial position.

    The ROD and PADDLEs rotate about the same axis and has no freedom to move relatively to SHAFT. The OFFSETs of ROD and both PADDLEs are zero.

    The movement of SHAFT object is a rotation clockwise about X plane. Rotation angle is described as

    
     (MOVOB of SHAFT is POS(0&0&0&360*tim&0&0))