Dof Managers

The DofManager class is the base class for all dof managers. Dof manager is an abstraction for object possessing degrees of freedom (DOFs). Dof managers (respectively derived clases, representing nodes or sides) are usually shared by several elements and are maintained by corresponding domain. The elements keep the logical reference to corresponding dof managers (they store their numbers, not the physical links). The base class declares the variable storing total number of DOFs, the dofArray representing the list of DOFs managed by dof manager, and loadArray list for storing the applied loadings references. The DofManager declares (and implements some of them) following services

• DOF management methods. The methods for requesting the total number of DOFs (giveNumberOfDofs), requesting particular DOFs (giveDof), assembling location array of code numbers (giveLocationArray and giveCompleteLocationArray), methods for DOF selection based on their physical meaning (giveDofArray and findDofWithDofId), and services for requesting unknowns related to dof manager DOFs (giveUnknownVector and givePrescribedUnknownVector).
• Transformation functions. The governing equations can be assembled not only in global coordinate system, but also in user-defined local coordinate system of each dof manager. Following methods introduce necessary transformation methods, allowing DOFs to be expressed in their own local c.s. or to be dependent on other dofs on other dofManager (to implement slave or rigid arm nodes etc.). The methods for computing transformation matrices from global c.s to receiver's defined coordinate system are declared (computeDofTransformation and computeLoadTransformation). The requiresTransformation indicates whether dofManager requires the transformation from global c.s. to dof manager specific coordinate system.
• Load management functions. The two methods are provided for handling applied loading - the service for computing the load vector of receiver in given time (computeLoadVectorAt) and service providing the list of applied loads (giveLoadArray).
• Context related services for storing/restoring the receiver state to context (saveContext and restoreContext services) are implemented.
• Instanciating service initializeFrom.
• Miscelaneous services for receiver printing, identification, etc.

In the OOFEMlib the common specialized dof managers are defined and implemented. Those currently provided are:

• Node class. Class implementing node in finite element mesh. Node manages its positon in space, and if specified, its local coordinate system in node. If local coordinate system is defined, all equilibrium equations are assembled in this system and therefore all DOFs and applied boundary and initial conditions apply in this local coordinate system. By default, global coordinate system is assumed in each node.
• RigidArmNode class. Class implementing node connected to other node (master) using rigid arm in finite element mesh. Rigid arm node supports not only slave dofs mapped to master but also some dofs can be primary doofs. The masterDofMask attribute is introduced allowing to distinguish between primary and mapped (slave) dofs. The primary DOFs can have their own boundary and initial conditions. The introduction of rigid arm connected nodes allows to avoid wery stiff elements used for modelling the rigid-arm connection. The rigid arm node maps its dofs to master dofs using simple transformations (small rotations are assumed). Therefore, the contribution to rigid arm node are localized directly to master related equations. The rigid arm node slave (mapped dofs can not have its own boundary or initial conditions, they are determined completely from master dof conditions. The local coordinate system in slave is not supported in current implementation, the global lcs applies. On the other hand, rigid arm node can be loaded independently of master. The transformation for DOFs and load is not ortogonal - the inverse transformation can not be constructed by transposition. Because of time consuming inversion, methods can generally compute both transformations for dofs as well as loads.
• ElementSide class - representing finite element side possesing some DOFs.