Wave Loading Calculator

Calculate wave forces on cylindrical structures using the Morison equation with linear (Airy) wave theory, including drag and inertia components.

Inputs

Design wave height (m)

Wave period (s)

Water depth (m)

Member diameter (m)

Evaluation depth (m)

Drag coefficient Cd

Inertia coefficient Cm

Seawater density (kg/m³)

Tab to move between fields

Results

Drag force (N/m)

969.92

Inertia force (N/m)

2,008.51

Combined force SRSS (N/m)

2,230.44

Max particle velocity (m/s)1.23

Max particle acceleration (m/s²)0.96

Wavelength (m)96.05

Keulegan-Carpenter number8.17

How to Use This Calculator

Enter design wave height (m), wave period (s), and still water depth (m).
Enter structural member diameter (m) and evaluation depth (m below surface, enter as negative).
Read wave kinematics: horizontal velocity (m/s), acceleration (m/s2), and wavelength (m).
Review inline force (kN/m) from the Morison equation — drag and inertia components.
Use peak force for structural design load cases and compare drag vs. inertia dominance.

How the result changes with Design wave height (m)

Design wave height (m)	Drag force (N/m)	Inertia force (N/m)	Combined force SRSS (N/m)
3.09	1,028.98	2,068.76	2,310.54
11	13,039.98	7,364.53	14,975.9
20	43,107.38	13,390.05	45,139.12
27	78,563.2	18,076.57	80,616

What each input means

Design wave height (m): Significant or maximum design wave height H in meters.
Wave period (s): Peak or design wave period T in seconds.
Water depth (m): Still water depth d from seabed to mean water level.
Member diameter (m): Outer diameter of the cylindrical structural member.
Evaluation depth (m): Depth below SWL to evaluate forces (0 = surface, negative = deeper).
Drag coefficient Cd: Morison drag coefficient; typical 0.6-1.2 depending on Re and roughness (DNV-RP-C205).
Inertia coefficient Cm: Morison inertia coefficient; typical 1.6-2.0 for smooth cylinders.
Seawater density (kg/m³): Density of seawater; ~1025 kg/m³ for typical ocean conditions.

What each result means

Drag force (N/m): Maximum drag force per unit length of member.
Inertia force (N/m): Maximum inertia force per unit length of member.
Combined force SRSS (N/m): Square root of sum of squares of drag and inertia — conservative peak estimate.
Max particle velocity (m/s): Maximum horizontal water particle velocity at evaluation depth.
Max particle acceleration (m/s²): Maximum horizontal water particle acceleration at evaluation depth.
Wavelength (m): Wavelength from the dispersion relation.
Keulegan-Carpenter number: KC = u*T/D. KC < 2 is inertia-dominated, KC > 20 is drag-dominated.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Design wave height (m) = 3, Wave period (s) = 8, Water depth (m) = 30, Member diameter (m) = 1.2 = 8 input(s) provided
Calculate Drag force
Drag force = 0.5 * Cd * rho * D * uMax * uMax
969.92 = 969.92
Calculate Inertia force
Inertia force = Cm * rho * (π * D * D / 4) * dudtMax
2008.51 = 2008.51
Calculate Combined force SRSS
Combined force SRSS = sqrt(fDrag * fDrag + fInertia * fInertia)
2230.44 = 2230.44
Calculate Max particle velocity
Max particle velocity = (π * H / T) * depthFactor
1.226 = 1.226
Calculate Max particle acceleration
Max particle acceleration = (2 * π * π * H / (T * T)) * depthFactor
0.963 = 0.963

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