Scene and nodes

How to set-up a scene using code

This is the main module of the engine. It contains both the nodes and the scene.

A node is an item or element in a model. For example a ship or a force. A Scene is a collection of nodes.

The common way of working is as follows:

1. Create a scene

2. Add nodes to it

Example:

s = Scene()                               # create an empty scene
s.new_poi('point 1')                      # creates a poi with name anchor
s.new_poi('point 2', position = (10,0,0)) # create a second poi at x=10
s.new_cable('line',poiA = 'point 1', poiB = 'point 2') # creates a cable between the two points
s.save_scene(r'test.dave')                # save to file

Nodes in a scene can be referenced by either name or by reference. The new_some_node_type functions return a reference to the newly created node.

s = Scene()
a = s.new_axis('axis')                     # a is now a reference to node 'axis'

p1 = s.new_poi('poi_1', parent = a )       # refer by reference
p2 = s.new_poi('poi_2', parent = 'axis' )  # refer by name

A reference to a node can also be obtained from the scene using square brackets:

s = Scene()
s.new_axis('axis')

a = s['axis']
print(a.position)

Node types

The following node types can be used:

Node-types

Icon	Type	Description
Geometry
	Axis Scene.new_axis()	Axis is an local axis system. This is the main building block of the geometry.
	Poi Scene.new_poi()	Point of interest is a position on an axis system. Used as connection point or reference point for other nodes.
	RigidBody Scene.new_rigidbody()	This is a rigid body with a mass and cog.It creates its own axis system (it is a super-set of Axis)
Connections
	DAVE.Scene.Cable Scene.new_cable()	Linear elastic cable between two or more pois
	LinearBeam Scene.new_linear_beam()	Linear elastic beam between two or more pois
	LC6d Scene.new_linear_connector_6d()	Connects two axis systems with six linear springs
	Connector2d Scene.new_connector2d()	Connects two axis systems with one rotational and one translational spring
Forces
	Force Scene.new_force()	This is a force/moment. If is defined in the global axis system and acts on a poi
	HydSpring Scene.new_hydspring()	Create linear springs to model linearized hydrostatics
	Buoyancy Scene.new_buoyancy()	Buoyancy mesh for non-linear, shape-based hydrostatics
Other
	Visual Scene.new_visual()	3D visual to spice-up the looks of the scene
	TriMeshSource Buoyancy.trimesh()	3D triangulated mesh for buoyancy calculations. Automatically created when a Bouyancy node is added.

Geometry is build using Axis systems, Rigid bodies and Pois.

Axis systems and rigid bodies have a position and an orientation. Pois only have a position

All can be positioned on a parent. If a node has a parent then this means that its position and orientation are expressed relative to that parent.

Axis and RigidBodies can have all their six individual degrees of freedom either fixed or free. If a degree of freedom is free then this means that the node is able to move/rotate in this degree of freedom.

If this is the first time you read this then please use the Gui to experiment.

Scene functions

Apart from methods to create nodes, Scene also harbours functionality to delete, import, re-order and export nodes.

Scene functions

Action	How	Description
Create a new scene	s = Scene()	Creates a new scene “s”. Optionally a file-name can be provided to load the contents of that file directly into the scene
Adding content
Adding a node	s.new_poi, s.new_axis, etc..	See list of node types and new_ functions in the next table.
Import nodes (1)	Scene.import_scene()	Imports all nodes from an other scene and places them as a group in the current scene.
Import nodes (2)	Scene.load_scene()	Imports all nodes from an other scene and adds them to the current scene. Beware of name-conflicts.
Access nodes
Get a node	s[‘node_name’]	gets a reference to a node with name “node_name”.
Get all nodes of a type	Scene.nodes_of_type()	gets a list of reference to all nodes with this type
Get all nodes that depend on	Scene.nodes_depending_on()	gets a list of reference to all nodes with this type
Get all child nodes	Scene.nodes_with_parent()	gets a list of reference to all nodes with this type
Deleting content
clear	Scene.clear()	Deletes all nodes from the scene
delete	Scene.delete()	Deletes a node from the scene. All nodes that depend on this node will be deleted as well.
dissolve	Scene.dissolve()	Removes a single node from the scene. Attempts to maintain child nodes. Often used in combination with import
Saving or exporting
Save to file	Scene.save_scene()	Saves the content of the scene to a file
Get as python code	Scene.give_python_code()	Returns python to re-create the scene in its current state.
Print node-tree	Scene.print_node_tree()	Prints a node-tree
Solving
Solve statics	Scene.solve_statics()	Brings the nodes in the scene to a static equilibrium
Goal seek	Scene.goal_seek()	Iteratively changes a property to set another property to some specified value.

Notes: rotations are defined as https://en.wikipedia.org/wiki/Axis%E2%80%93angle_representation#Rotation_vector