Buoyancy and Water Physics Simulation in R3F

Act as a Simulation Programmer. Describe the complex mathematical implementation required to simulate realistic buoyancy for standard RigidBodies submerged within a virtual fluid volume in a React Three Fiber scene. You must script a custom physics tick that calculates the upward force vector based strictly on Archimedes' principle (displaced volume multiplied by [FLUID_DENSITY]). Simultaneously apply a heavy, velocity-dependent [DRAG_COEFFICIENT] vector to aggressively simulate physical water resistance the millisecond an object's Y-coordinate drops below the defined [WATER_LEVEL]. Detail exactly how to hook into the custom `useFrame` loop to apply these `applyImpulse` or `addForce` methods manually to Rapier bodies without breaking the engine's internal step logic.