Spring

模拟点被弹簧连接着的行为。

Spring会给每个点指定一个质量，并在点上模拟力的效果（重力，风，纹紊乱）。每个点会像弹簧那样，试图返回到其原始位置处。

You can:

使用节点上的Fix Point参数，配合一个点组，使网格特定的点停留在固定位置处。

使用力选项卡中的参数，给点运用方向力，阻力，紊乱力。

连接一个Force SOP到第三输入端，可以让你使用变形球吸引，或排斥粒子。

Tip

阻力值越大，或质量越小，步频消亡会越快。

Note

S平日们好 SOP可以用于模拟很多效果，但是对于复杂精致的模拟，可使用刚体，布料，或线动力学。

Note

如果输入的数据中，有点法线属性，但没有点速度属性，Spring 节点会使用点的法线作为初始点的速度。如果你像点上添加速度属性，点法线会被忽略。

Parameters

State

StartTime	Time at which the simulation resets.
Preroll Time	Number of initial frames skipped.
Time Inc	Time per iteration.
Accurate Moves	Particles move more accurately.
Attractor Use	How the attractor points affect particles All points All points affect each particle Single point per particle Only one point affects each particle

Forces

External Force	Force of gravity on points.
Wind	Wind force acting on points.
Turbulence	Amplitude of turbulence along axes.
Turb Period	Inverse variance of turbulence over space.
Seed	Seed for random turbulence generator.

Nodes

Fixed Points	Group of points not to be moved by this operation.
Fixed Points go to Source Positions	Fixed Points are put to their positions in the Source.
Copy Groups from Source	All Source groups are copied at each frame. Useful if the Fixed Points group contents are animated.
Add Mass Attribute	Causes point mass to be calculated.
Mass	Relative mass of each point.
Add Drag Attribute	Causes drag coefficient to be calculated.
Drag	Drag of each point.
Spring Behavior	How the springs will behave Hooke’s Law Use Hooke’s law. Force = displacement x spring constant. Normalize Displacement Like Hooke’s law except displacement is normalized to the original length of the spring. (Behavior used in Houdini 2.5).
Spring Constant	Stiffness of the spring
Initial Tension	Initial spring tension before deformations.

Limits

+ Limit Plane, – Limit Plane	Points die or bounce off limit planes on contact. /limitposx … /limitposz, /limitnegx …
Hit Behavior	Whether particles die or bounce on limit planes.
Gain Tangent	Energy loss tangent to the collision.
Gain Normal	Energy loss perpendicular to the collision.

Inputs

Spring Source	The points to simulate, for example a polygon sphere or mesh.
Collision Object	(Optional) Geometry for the points to collide with. When the points hit this geometry, they can stick or bounce. If the collision object is deforming, collision detection may fail, causing some points to leak through the collision geometry.
Force	(Optional) A Force SOP, which uses a metaball to create a field which attracts or repels the points.