Class XpbdWorld<T>

Example

import { XpbdWorld } from '@datamoc/mwg/physics/xpbd';

const world = new XpbdWorld({ gravity: 520 });
const wall = world.addNode({ x: 0, y: 0, fixed: true });
const weight = world.addNode({ x: 40, y: 0, mass: 1 });
const rope = world.addLink({ a: wall, b: weight, stiffness: 2e4, strength: 900 });
world.breaking = true;
for (let i = 0; i < 120; i++) world.step();
console.log(world.links[rope].broken, world.nodes[weight].y > 0);
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A bridge is a truss: beams are links, a cable is a link with tensionOnly: true (it pulls when stretched and goes slack when pushed), and a link with a strength breaks at that load. A bare chain of planks has no vertical stiffness and only sags like a rope, so the deck needs triangles.

Example

import { XpbdWorld } from '@datamoc/mwg/physics/xpbd';

//a Warren truss between two abutments, with a cart of `cartMass` at midspan
function loadBridge(cartMass: number): { sag: number; broken: number; peakLoad: number } {
	const world = new XpbdWorld({ gravity: 520 });
	const spacing = 50;
	const bottom: number[] = [];
	for (let i = 0; i <= 6; i++) bottom.push(world.addNode({ x: i * spacing, y: 0, fixed: i === 0 || i === 6 }));
	const top: number[] = [];
	for (let i = 0; i < 6; i++) top.push(world.addNode({ x: i * spacing + spacing / 2, y: -45 }));

	const beam = (a: number, b: number): void => {
		world.addLink({ a, b, stiffness: 6e4, strength: 16000 });
	};
	for (let i = 0; i < 6; i++) beam(bottom[i], bottom[i + 1]); //the deck
	for (let i = 0; i < 5; i++) beam(top[i], top[i + 1]); //the upper chord
	for (let i = 0; i < 6; i++) {
		beam(bottom[i], top[i]); //the diagonals
		beam(top[i], bottom[i + 1]);
	}

	//the cart rests on the deck and the chord; without a `strength` its links cannot break
	const cart = world.addNode({ x: 150, y: -6, mass: cartMass });
	world.addLink({ a: cart, b: bottom[3], stiffness: 6e4 });
	world.addLink({ a: cart, b: top[2], stiffness: 6e4 });

	world.breaking = true;
	for (let i = 0; i < 360; i++) world.step();
	return {
		sag: Math.max(...bottom.map((node) => world.nodes[node].y)),
		broken: world.links.filter((link) => link.broken).length,
		peakLoad: Math.max(...world.links.map((link) => link.ratio)), //1 is the breaking point
	};
}

console.log(loadBridge(2)); //holds, a little sag
console.log(loadBridge(20)); //too heavy: beams break
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