Bouncing speed problem..

Hey guys, I've posted a thread about buoyancy, I've made it myself, but now I'm over a pretty simple problem, that I just can't figure out for days.
I have a Plane that represents my water surface, I have a cube with a rigidbody attached to it.
When I drop my rigidbody in the water it starts to float as expected.

My problem is that the rigidbody looses energy during bouncing up and down, and when it reach a point where the distance between the lifting force is almost equal to the dragging force, the cube is shaking up and down with a very fast speed.
How can I make it look smoother?
I tried to use Vector3.lerp, but it didn't work at all... (Or I don't use it correctly..)

Here's my code:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class physBuoyancy2 : MonoBehaviour {
5.  
6.  
7.     float waterLevel;
8.     float floatHeigth = 2f;
9.     float bounceDamp = 0.05f;
10.     float forceFactor;
11.  
12.     Vector3 buoyancyCenterOffset;
13.     Vector3 actionPoint;
14.     Vector3 upLift;
15.  
16.     float cubeDensity = 0.65f;
17.     float liquidDensity = 1f;
18.     float waterHeight;
19.  
20.     float forceOfGravity;
21.     float buoyancyForce;
22.     float dragForce;
23.  
24.     Bounds cubeBounds;
25.     float displacedWater;
26.     bool inWater;
27.  
28.     Vector3 currentVelocity;
29.     Vector3 oppositeVelocity;
30.     float boxDepth;
31.     float boxHeight;
32.     float boxWidth;
33.     float NetForce;
34.  
35.     // Use this for initialization
36.     void Start () {
37.         GameObject mesh = GameObject.FindWithTag ("waterPlane");
38.        
39.         GameObject droppingBox = GameObject.FindWithTag("droppingBox");
40.  
41.         Mesh meshFilter = mesh.GetComponent<MeshFilter>().mesh;
42.         Bounds bounds = meshFilter.bounds;
43.        
44.        
45.         Mesh meshBox = droppingBox.GetComponent<MeshFilter> ().mesh;
46.         cubeBounds = meshBox.bounds;
47.  
48.         boxDepth = cubeBounds.max.z - cubeBounds.min.z;
49.         boxHeight = cubeBounds.max.y - cubeBounds.min.y;
50.         boxWidth = cubeBounds.max.x - cubeBounds.min.x;
51.  
52.         waterHeight = 5f;
53.         displacedWater = boxWidth * boxHeight * Mathf.Clamp (waterHeight - (rigidbody.position.y - boxHeight * 0.5f), 0, boxHeight);
54.  
55.  
56.     }
57.    
58.     // Update is called once per frame
59.     void Update () {
60.         dragForce = 0f;
61.  
62.         if(rigidbody.position.y < 0f){
63.             calculateBuoyancy ();
64.  
65.             dragForce = -0.5f * (rigidbody.velocity.y * rigidbody.velocity.y) * liquidDensity * (boxWidth * boxDepth) * 1.33f;
66.        
67.             if (rigidbody.velocity.y < 0)
68.                 dragForce *= -1;
69.  
70.             NetForce = forceOfGravity + buoyancyForce + dragForce;
71.  
72.             Vector3 nForce = Vector3.up * NetForce;
73.  
74.             rigidbody.AddForce(nForce);
75.  
76.         }
77.  
78.  
79.     }
80.  
81.     void OnTriggerEnter(Collider collider){
82.         inWater = true;
83.         rigidbody.drag = 2f;
84.     }
85.  
86.     void calculateBuoyancy(){
87.         forceOfGravity = rigidbody.mass * Physics.gravity.y;
88.         buoyancyForce = displacedWater * liquidDensity * (-Physics.gravity.y);
89.  
90.     }
91.  
92. }
93.  

 

If two small but opposite forces cause a glitch, the solution would be to forcibly set them to zero. Something like: if lifting is almost equal to dragging AND both lifting and dragging are small, set them both to zero.

 

When I set them to 0, my objects are sinking to the bottom. :/

 

How about setting them to be precisely equal?

 

Code (CSharp):

1. currentPosition = rigidbody.position;
2.             Debug.Log(currentPosition - previousPosition);
3.             if((currentPosition.y - previousPosition.y) <= 0f){
4.                 forceOfGravity = buoyancyForce;
5.             }
6.  
7.             NetForce = forceOfGravity + buoyancyForce + dragForce;
8.  
9.             Vector3 nForce = Vector3.up * NetForce;
10.  
11.             rigidbody.AddForce(nForce);
12.             previousPosition = currentPosition;

This is what I'm doing, and it's still glitching.. (if you meant someting like this)

 

I think you have to move the line calculating displacedWater in calculateBuoyancy() because it can change when near the surface.

 

Hm, I guess you're right, now the cubes are bouncing in bigger distance, but when they reach a certain value, they just return to the starting bouning value. Is there a way to make the bouncing movement smoother (slower) and to prevent the continuous bouncing?

 

The way is... understand WHY they are bouncing then find a way to fix it.

I tryed your script on a box but it float with no gravity if position.y is something between >0 and 5, and fall with gravity if y < 0. No bouncing at all but probably I am missing something in the scene setup.

 

For the cube to float, you need to change it's density by lowering the cube's mass From 0 to 0.4 it floats, from 0.5 above it sinks. Then when position.y < 0, it'll change the direction of the drag force.
I think this is the only thing in the editor..

You're right about the understanding part, but I'm stuck on this one from quite some time, so I decided to ask a guru, so I've posted.

 

For values of mass like .15 you have a fun behaviour with continuos bouncing of some meters...

If you change the line in Update() with this, it stop bouncing:

if ((rigidbody.position.y - boxHeight * 0.5f) < waterHeight) { // when the box bottom is underwater...

Perhaps you can also not limit the dragForce on the Y axis, if you want a bit more of realism. Anyway you dont need to also change rigidbody.drag in OnTriggerEnter .

 

If at 0.5 mass it sinks is because you use forceOfGravity with rigidbody.useGravity at the same time. Without 2 times gravity a cube sink at about 1.21 mass instead of 1, because you have to apply forces in FixedUpdate().

I ended up with this:

Code (CSharp):

1.     void FixedUpdate ()
2.     {
3.         if((rigidbody.position.y - boxHeight * 0.5f) < WaterHeight)
4.         {
5.             calculateBuoyancy ();
6.            
7.             dragForce = 0.5f * rigidbody.velocity.sqrMagnitude * liquidDensity * (boxWidth * boxDepth) * .33f;
8.  
9.             Vector3 nForce = Vector3.up * buoyancyForce + dragForce * -rigidbody.velocity.normalized;
10.             rigidbody.AddForce(nForce);
11.         }
12.     }

 

Great work, and thank you very much, the bouncing seems pretty smooth right now.
I never saw this.
Btw, I figured out that I was calculating magnitude wrong.
And after the correction the bouncing appeared where we wanted it to be, here is the change in the start function:

Code (CSharp):

1. boxDepth = Mathf.Sqrt(Mathf.Pow(cubeBounds.max.z, 2.0f) + Mathf.Pow(cubeBounds.min.z, 2.0f));
2.         boxHeight = Mathf.Sqrt( Mathf.Pow(cubeBounds.max.y, 2.0f) + Mathf.Pow(cubeBounds.min.y, 2.0f) );
3.         boxWidth = Mathf.Sqrt( Mathf.Pow(cubeBounds.max.x, 2.0f) + Mathf.Pow(cubeBounds.min.x, 2.0f));

 

I just ignored the start function and set the box manually but thanks. I'll give it a try.

 

I wonder why you dont simply use cubeBounds.size but I wonder more if your last code works.
Perhaps I am missing something...

Edit: I think you are using a cube larger (taking diagonal dimensions) perhaps to compensate for the lower drag after I changed the cx value from 1.33f to .33f (to simulate something more like a ball than a box).

I was wondering of your code because I was thinking to bounds in worldspace... but I see it's local for the mesh.

 

Sorry for the ugly code, I will try to describe how I set my stuff:

Code (CSharp):

1. float cubeDensity = 0.65f;
2.     float liquidDensity = 1f;
3.     float waterHeight;
4.  
5.     float forceOfGravity;
6.     float buoyancyForce;
7.     float dragForce;
8.  
9.     Bounds cubeBounds;
10.     float displacedWater;
11.     bool inWater;
12.  
13.     Vector3 currentVelocity;
14.     Vector3 previousVelocity;
15.     Vector3 oppositeVelocity;
16.     float boxDepth;
17.     float boxHeight;
18.     float boxWidth;
19.     float NetForce;
20.  
21.     // Use this for initialization
22.     void Start () {
23.         GameObject mesh = GameObject.FindWithTag ("waterPlane");
24.         //GameObject mesh2 = GameObject.FindWithTag ("waterBottom");
25.         GameObject droppingBox = GameObject.FindWithTag("droppingBox");
26.  
27.         Mesh meshFilter = mesh.GetComponent<MeshFilter>().mesh;
28.         Bounds bounds = meshFilter.bounds;
29.        
30.         float waterDepth = Mathf.Sqrt(Mathf.Pow(mesh.transform.position.y, 2.0f) + Mathf.Pow(-5f, 2.0f));
31.         float waterLength = Mathf.Sqrt(Mathf.Pow(bounds.min.x, 2.0f) + Mathf.Pow(bounds.max.x, 2.0f));
32.         float waterWidth = Mathf.Sqrt(Mathf.Pow(bounds.min.z, 2.0f) + Mathf.Pow(bounds.max.z, 2.0f));
33.        
34.         Mesh meshBox = droppingBox.GetComponent<MeshFilter> ().mesh;
35.         cubeBounds = meshBox.bounds;
36.  
37.         boxDepth = Mathf.Sqrt(Mathf.Pow(cubeBounds.max.z, 2.0f) + Mathf.Pow(cubeBounds.min.z, 2.0f));
38.         boxHeight = Mathf.Sqrt( Mathf.Pow(cubeBounds.max.y, 2.0f) + Mathf.Pow(cubeBounds.min.y, 2.0f) );
39.         boxWidth = Mathf.Sqrt( Mathf.Pow(cubeBounds.max.x, 2.0f) + Mathf.Pow(cubeBounds.min.x, 2.0f));
40.  
41.         waterHeight = 0.05f;
42.         //displacedWater = boxWidth * boxHeight * Mathf.Clamp (waterHeight - (rigidbody.position.y - boxHeight * 0.5f), 0, boxHeight);
43.     }
44.    
45.     // Update is called once per frame
46.     void FixedUpdate () {
47.         dragForce = 0f;
48.  
49.         if(((rigidbody.position.y - boxHeight) * 0.5f) < waterHeight){
50.             calculateBuoyancy ();
51.  
52.             //Fd = (1/2) * v ^ 2 * fluidDensity * ( area ) * dragCoefficient
53.             dragForce = 0.5f * rigidbody.velocity.sqrMagnitude * liquidDensity * (boxWidth * boxDepth) * 1.33f;
54.  
55.             //if ((rigidbody.position.y - boxHeight * 0.5f) < waterHeight)
56.             //    dragForce *= -1f;
57.  
58.             //NetForce = forceOfGravity + buoyancyForce + dragForce;
59.  
60.             Vector3 nForce = Vector3.up * buoyancyForce + dragForce * (-rigidbody.velocity.normalized);
61.  
62.                 rigidbody.AddForce(nForce);
63.            
64.  
65.         }
66.  
67.  
68.     }
69.  
70.  
71.     void calculateBuoyancy(){
72.         displacedWater = boxWidth * boxHeight * Mathf.Clamp (waterHeight - (rigidbody.position.y - boxHeight * 0.5f), 0, boxHeight);
73.  
74.         forceOfGravity = rigidbody.mass * Physics.gravity.y;
75.         buoyancyForce = displacedWater * liquidDensity * (-Physics.gravity.y);
76.  
77.     }
78.  
79. }

I've returned the drag coef to 1.33f because my boxes jumped out of the water when I their mass is too low. Just like a ball would.

My cube is with a scale factor of 1, and it usualy has aroud 1.90 to 2 mass. (If it's greater than 2 it will bounce underwater which is not what should exactly happen, It has to sink)
If this is not enough I will attach my full project, it's not a problem for me.

 

I just wanted to be sure you know that if you have a cube 1x1x1, cubeBounds.size return a Vector3 (1, 1, 1) while your code return a cube of 1.4x1.4x1.4.