The Force operator allows you to apply various forces to particles.
X/Y/Z: controls the direction vector of the wind.
Strength: controls the strength of the wind.
Source vector: controls the input vector used to calculate the noise values.
Channel: the custom data channel to read custom vectors from.
Affect magnitude/direction/both: controls which aspects of the resulting particle velocity the forces will affect.
X/Y/Z %: controls the amount of influence forces will have over each axis of the resulting velocity.
Multiplier %: an overall multiplier applied to the resulting force values.
X/Y/Z %: controls the amount of influence forces will have over each axis of the resulting spin.
Multiplier %: an overall multiplier applied to the resulting force values.
When applying forces to spin values, the influence percentage may need to be very high to get the desired affect, due to the fact that spin is calculated in degrees per second and velocity is calculated in scene units per time step.
Seed: the seed value for all varied parameters.
The relative property multiplier will adjust values based on the ratio between the value of a particle property and the specified threshold value.
Property type: the particle property to which the threshold value will be compared.
Threshold: the target value to which the selected property value of a particle will be compared.
Min multiplier: the minimum value of the resulting multiplier.
Max multiplier: the maximum value of the resulting multiplier.
Exponent: the exponent to which the ratio between the particle property and the selected property will be raised.
The ‘relative to perpendicular surface area’ option will reduce the amount of force applied to a particle, depending on how close a particle’s shape mesh faces are to being perpendicular to the force being applied. In simpler terms: for each face of a particle mesh, if the faces is pointing towards (parallel) the force being applied , it will be affected by the force more than if the face is pointing perpendicular (away) from the force being applied. The amount each face will be influenced by the force, based on this calculation, is then summed up to create an overall force multiplier for each particle. This is a simple way to approximate certain aerodynamic effects.
The built-in gravity force is not affected by the ‘relative to perpendicular surface area’ setting.
The lower the threshold value, the less parallel face coverage is required in order to undergo full force influence.
Exponent: the relative surface area multiplier will be raised to this exponent. Higher values mean less perpensicular coverage will result in less force application.
Relative %: the percentage of affect the ‘relative to perpendicular surface area’ setting will have on the final result.
Simulate substeps: forces will be interpolated in a way that simulates the addition of forces at smaller simulation substeps.
Cloth aerodynamics: when enabled, cloth particles affected by the Force operator will have their force influences adjusted based on the angle between the force velocity and the face normals of the cloth that they are part of.
The closer the angles are to being coincident, the higher the influence the force will have on the cloth particles. This helps to simulate cloth ripples and other aerodynamically-accurate effects.
The higher the value, the closer the cloth face normal angles must be to the force velocities in order for the velocities to affect the cloth particles. In technical terms, this is the exponent which the dot product between the force vector and the face normal is raised to, before being used as a multiplier for the overall force influence amount on a particular particle.