File elasticJoint.h

class elasticJoint

Public Functions

elasticJoint(int node, int limb_idx, const vector<shared_ptr<elasticRod>> &limbs)

Constructor for initializing an elastic joint.

Parameters:

node – The node on the elastic rod that will be converted to a joint.
limb_idx – The limb id of the rod.
limbs – Container of limbs.

void addToJoint(int node_num, int limb_idx)

Adds a connection to the joint.

When we connect a node to a joint, that node is actually “replaced” with the joint node. Therefore, we assume that nodes that are connected to a joint have positional overlap.

Parameters:

node_num – The id of the node that is being replaced by the joint node.
limb_idx – The limb id of the replaced node.

void updateJoint()

Updates the positions and velocities of the joint node.

All positions and velocities are computed within elasticRod. Therefore, before we compute anything within the elasticJoint class, we need to copy over the correct positions and velocities.

void updateRods()

Updates the positions of the “replaced” nodes in other limbs.

Recall that when attaching a rod to an existing joint, the overlapping node is “replaced” with the joint node. Behind the scenes, this node actually still coexists with the joint node. Therefore, for certain computations within elasticRod not to be incorrect, we need to update the position of the “replaced” node to match the joint node.

void updateConnectedNodes(int node_num, int limb_idx, bool remove_dof)

A helper function to store miscellaneous info when the joint is updated.

Parameters:

node_num – The id of the node that is being replaced by the joint node.
limb_idx – The limb id of the replaced node.
remove_dof – Whether the node is being attached to a preexisting joint. For example, this value should only be False for the very first node being converted to a joint node at initialization.

void prepLimbs()

void prepareForIteration()

void setup()

Public Members

int joint_node: The node id of the joint.

int joint_limb: The limb id of the joint.

int ne: Total number of edges that connect to this joint.

vector<shared_ptr<elasticRod>> limbs: The stored limbs of the simulation.

Vector3d x0: The position of the joint node from the previous timestep.

Vector3d x: The position of the joint node during and after the current timestep.

Vector3d x_ls: Position vector used to save state during line search.

Vector3d u0: Velocity vector from the previous timestep.

Vector3d u: Velocity vector during and after the current timestep.

vector<pair<int, int>> connected_nodes

Container storing the ids of all nodes that have an edge connection to the joint node.

First value is the node id Second value is the limb id

vector<pair<int, int>> replaced_nodes

Container storing the ids of all the replaced nodes.

First value is the node id Second value is the limb id

vector<int> bending_twist_signs

The direction of the tangent of each edge connected to the joint node, used to compute bending and twisting force signs.

For each edge connected to the joint node, a value is stored to keep track whether the tangent of the node goes toward the joint node or out of the joint node. This direction of the tangent is determined when each rod is initialized. A value of 1: the tangent is going into the joint node. A value of -1: the tangent is going out from the joint node.