Question 1

What is Archimedes' principle and the buoyancy formula?

Accepted Answer

Archimedes' principle states that the buoyant force on an object equals the weight of the fluid it displaces. The formula is F_b = ρ_f · g · V_sub, where ρ_f is the fluid density, g is gravitational acceleration (9.81 m/s²), and V_sub is the submerged volume. For a fully submerged object, V_sub equals the total volume of the object.

Question 2

How do you determine whether an object will float or sink?

Accepted Answer

Compare the object density ρ_obj with the fluid density ρ_f. If ρ_obj < ρ_f, the object floats; if ρ_obj > ρ_f, it sinks; if they are equal, the object achieves neutral buoyancy and remains stationary at any depth. For example, wood (~500 kg/m³) floats in water (1000 kg/m³), while iron (~7800 kg/m³) sinks.

Question 3

How is apparent weight (underwater weight) calculated?

Accepted Answer

Apparent weight = actual weight W minus buoyant force F_b. In formula form: W_app = (ρ_obj − ρ_f) · g · V_sub. A positive apparent weight means the net force still acts downward (object tends to sink), while a negative value means the net force acts upward (object tends to float). This concept is essential for underwater weighing, submersible design, and ballast calculations.

Question 4

How can this tool be applied in CAE and fluid simulation?

Accepted Answer

Key applications include: (1) Initial buoyancy balance checks for floating structures and submersible equipment design; (2) Quick estimates for particle or bubble behavior in fluid (CFD preprocessing); (3) Ship draft calculation and cargo capacity estimation; (4) Subsea structure installation calculations (cables, pipelines). Archimedes' principle underpins the buoyancy source term in CFD codes such as OpenFOAM and ANSYS Fluent.

Buoyancy Calculator

Theory