Scenario: a tank in a fire

A sealed steel tank of gas stands beside a crate. A fire burns under it. The wall warms, the gas warms with it, the pressure rises with the absolute temperature, and when the pressure passes what the shell holds the tank bursts: an air blast with a steel casing that flies apart. The crate nearby is pushed. This is the BLEVE that fire services plan around, and it needs no special code: five packages, three of which never heard of each other.

The chain#

Building it#

The wall is a heat part with a constant power standing for the flame. The gas is a GasVolume, and gasInPart joins the two with a conductance in W/K:

const net = new HeatNetwork();
const wall = net.addPart({ name: 'wall', mass: 40, material: steel, T: 293.15, power: 20e3 });
const gas = new GasVolume({ moles: 8, temperature: 293.15, volume: 0.2 });
const link = gasInPart(gas, wall, net, 200);
const burstPressure = 4 * gas.pressure;

Each step moves the heat and watches the one number the rule needs:

net.step(dt);
link.step(dt, host, []);
if (gas.pressure > burstPressure) {
  blast.detonate({ at: tankPosition, vessel: { pressure: gas.pressure, volume: 0.2, gamma: 1.4 },
                   burst: 'air', casing: { mass: 30, shape: 'cylinder' } });
}

What happens#

With 20 kW into a 40 kg steel wall the gas takes a few minutes to reach four times its fill pressure. At constant volume that means four times the absolute temperature, so the wall is by then well past red heat. The burst fires explosion:blast and then explosion:fragments on the world's event bus, and the crate beside the tank leaves with a velocity from the blast.

What the capabilities said to each other#

• Heat to gas. gasInPart moves G (T_wall − T_gas) dt joules from the wall to the gas each step; the wall pays what the gas takes, so the pair keeps its energy. Heat has no pressure model; pressure is the gas's n R T / V.
• Gas to rule to blast. The only logic you write is pressure > limit. The energy of the burst is the gas's expansion work (p − p₀) V / (γ − 1), converted to kilograms of TNT by the explosions capability (the vessel branch of detonate).
• Blast to bodies. The crate gets I · A at its distance (and less if something shields it); the casing becomes fragments that leave at the Gurney velocity and, if a wall has the armour value, are stopped or pass by their energy.
• Time. The fire is the only clock: with 20 kW and a 40 kg steel wall it takes minutes; with 200 kW, seconds. Change power to see the margin an extinguisher or a relief valve buys.

Variations#

The complete run, with the numbers it must produce, is in tests/unit/examples/physics-scenarios-tank-fire.test.ts.