For the graph-The red line (𝑓d) is the superposition of drag (blue) and inertia (green) forces. Since drag ∝ velocity and inertia ∝ acceleration, their peaks occur at different times. As a result, 𝑓x varies over the cycle and its maximum is not simply the sum of the individual peak values

In the Morison equation (𝑓ₓ = 𝑓_dₓ + 𝑓ᵢₓ), we’re adding drag and inertia forces. This works well for slender structures where D/λ is small, meaning diffraction effects are minimal — the waves mostly pass by without being strongly disturbed

Inertia term (2nd) ∝ significant in oscillatory flow.

Drag term (1st) ∝ dominates in high-speed flow