Server Example: Heavy Objects on Cloth

Overview

Three loads rest on cloth: a 10 kg ball on a cloth on the ground, a 5 kg box on two stacked cloths, and a 5 kg blanket draped over a 1 kg box. The cloth is solved together with the bodies (World::setMonolithicDeformables()), so each load rests on what carries the cloth: the ball and the box on the ground through the cloth, and the blanket on the box, which carries the blanket's weight to the ground. Every five seconds the world starts over, and the example prints how far each load pressed into what carries it.

Load	Default coupling	Solved together
Cloth under the 10 kg ball, pressed into the ground	10.8 mm	< 0.001 mm
Upper cloth under the 5 kg box, pressed into the lower one	18 mm	0.4 mm
1 kg box under the 5 kg blanket, pressed into the ground	30 mm	0.03 mm

Solved together, the scene also steps faster (3.3 ms instead of 4.8 ms per 1 ms step on a Ryzen 9 3950X), since the contacts under the loads settle in fewer iterations.

Target

CMake target: heavy_objects_on_cloth.

Run

Run the build-tree executable and connect rayrai_tcp_viewer to port 8080:

./build-examples/examples/heavy_objects_on_cloth

On Windows, run build-examples/bin/heavy_objects_on_cloth.exe instead.

Details

• The cloths are particle meshes with nearly inextensible edges and a bending modulus of 1e-4 N m; their particles collide as 8 mm spheres. The cloth under the ball is 0.64 m square and weighs 0.2 kg; the stacked cloths are 0.32 m square and weigh 0.1 kg each, the blanket is 0.5 m square.
• The ball and the box are dropped from a few centimetres; the blanket falls 20 cm onto the box and drapes over its edges to the ground.
• The scene lives in include/heavy_objects_on_cloth.hpp, so the same scene can run without a viewer (Scene::Step()), as the RaiSim test of the example does.