About wind vector field simulation

Hi Wei,

Sorry, I understand what you're asking now - thanks for bearing with me!

Our demo for flow around a cylinder uses a custom FluidZone, not the default one. We wrote a velocity function specifically for that demo which looked at the cylinder object and created a flow field based on the free stream velocity and the rotation of the cylinder. That particular code wasn't released with the AO package and my colleague is on leave at the moment so I don't have access to the code he wrote. We are working on releasing more features and tools for flow simulation in the next update to AO.

I have thrown together a quick example of how you can go about this. Please only consider this as an example, I can't guarantee that it's accurate and working for all cases but it does give something that looks appropriate.

The example code:

using AerodynamicObjects;
using UnityEngine;

public class RotatingCylinderFluidZone : FluidZone
{
public AeroObject cylinder;

    public float freeStreamVelocity = 1;

    public override Vector3 VelocityFunction(Vector3 position)

    {

        // Get the position relative to the cylinder's position
        position -= cylinder.transform.position;

        // Assuming the cylinder is extruded along the z axis for simplicity

        float radialDistanceSquared = (position.x * position.x) + (position.y * position.y);
        float radialDistance = Mathf.Sqrt(radialDistanceSquared);
        float cylinderRadius = 0.5f * cylinder.dimensions.x;

        // Non-physical, we're inside the cylinder

        if (radialDistance <= cylinderRadius)

        {

            return Vector3.zero;

        }

        float cosTheta = position.x / radialDistance;
        float sinTheta = position.y / radialDistance;
        float omega = cylinder.rb.angularVelocity.z;
        float circulation = -omega * cylinderRadius * 2f * Mathf.PI * cylinderRadius;
        float rr = cylinderRadius * cylinderRadius / (radialDistance * radialDistance);

        float vr = (freeStreamVelocity - rr) * cosTheta;
        float vtheta = (-(freeStreamVelocity + rr) * sinTheta) - (circulation / (2f * Mathf.PI * radialDistance));

        return new Vector3((vr * cosTheta) - (vtheta * sinTheta), (vr * sinTheta) + (vtheta * cosTheta));

    }

}

I hope that's helpful!

A side note, the communication between AeroObjects and FluidZones is one way, i.e. an AeroObject gets flow information from a FluidZone but a FluidZone does not get information about AeroObjects.

Best,

Conor

Hi Conor,

Thank you for your assistance in enabling me to achieve the effect of the FluidZones interacting with the cylinder and producing airflow variations.

It was very helpful in achieving the desired effect of the flow field interacting with the cylinder and producing airflow variations.

However, my ultimate goal is to simulate airflow around irregular shapes. I was wondering if there is a solution for the flow field to interact with irregular models as well.

Thank you for your assistance,

Wei

Hi Wei,

Apologies for the delay. Simulating airflow around generic/irregular shapes is a job for a CFD package and is a bit beyond our aerodynamics tools. You can make an approximation in our tools by adding simple shapes together which would be enough to get a reasonable wake behind a vehicle etc. If you are feeling brave you could create functions for the flow around complex shapes and include them in a custom fluid zone, perhaps by modelling data from experiments.

Best wishes,

Conor

Hi Conor,

I saw your implementation of a wind simulation in the following demo on https://play.unity.com/en/games/ebfc045e-0126-4ea5-bc86-ba085b65cefe/ao-spinning-cylinder-custom-fluid-effector.

I would like to recreate a similar effect, but I noticed that when I interact with the FluidZone, the wind direction does not change based on the objects I come into contact with.

Therefore, I'm thinking of using the OnTriggerEnter method to detect if the FluidZone is collides with objects and updating the wind direction using windVelocity.GetVelocity() method.

And I also plan to add particle fields for visual simulation of the wind.

I'm not sure if my approach is correct.

Thank you so much for your help.

BR, Wei

Hi Wei,

I'm not sure I understand what you mean when you say "the wind direction does not change based on the objects I come into contact with". The demo you shared has a fluid zone which is connected to the cylinder by a public reference, i.e.

public AeroObject cylinder;

We then used properties of the cylinder in the VelocityFunction to create a mathematical representation of the wind speed in the space around the cylinder. A separate Flow Field Particles object is then placed inside that fluid zone and each particle has its velocity set by the zone's VelocityFunction, using the position of the particle as input.

Best,

Conor

Hi Conor,

I'm trying to use this approach, but I'm confused because the default fluid zone collides with the aero object sphere and is unable to react to the normal physical wind direction and velocity .

as this screenshot.

Rewritten VelocityFunction

public override Vector3 VelocityFunction(Vector3 position)

{

Vector3 uniformFluidVelocity = windVelocity.GetVelocity();

if (!enableTurbulence)

{

return uniformFluidVelocity;

}

position *= turbulenceLengthScale / referenceLength;

float time = Time.time * turbulenceTimeScale;

return new Vector3(uniformFluidVelocity.x + 2f * windVelocity.speed * turbulenceMagnitude * (Mathf.PerlinNoise(position.y + time, position.z + time) - 0.5f),

uniformFluidVelocity.y + 2f * windVelocity.speed * turbulenceMagnitude * (Mathf.PerlinNoise(position.x + time, position.z + time) - 0.5f),

uniformFluidVelocity.z + 2f * windVelocity.speed * turbulenceMagnitude * (Mathf.PerlinNoise(position.x + time, position.y + time) - 0.5f));

}

And in the LateUpdate method of FlowPointParticles.cs, the particle positions are used as input to the VelocityFunction."

particle.velocity+=fluidZones[j].VelocityFunction(particle.position);

Sorry, I'm a beginner with Unity. I'm not sure where I'm making mistakes or if there's something I've overlooked. Please let me know.

Thank you very much!