Seakeeping analyses

 

 

What can be done in the way of design,evaluation and verification - for owners, operators, agents, shipyards, consultants?

 

Assess effects of hull/load variations on seakeeping performance early in the design of new ships

For existing ships, analyse new routes or operational problems, or compare several ships for a proposed route

Direct computations are cost- and time-efficient

Dynamic results can be visualised on the screen, up to 4 hulls at a time

 

 

Seakeeping performance - motions, accelerations, operability, regularity

 

Seakeeping performance affects:

 

comfort and safety of passengers and crew

loads on equipment, cargo and structure

speed loss and service operability

 

Unsuitable hull forms or incorrect distribution of cargo will usually result in delays, cancellations or severe motions. In the worst cases, extreme vessel response can lead to passenger and crew injuries, movement of cargo, or damages to the ship's structure and equipment.

 

Direct computations provide relevant information about ship performance in a seaway, including physically realistic simulations of ship-wave problems. Anti-roll fins, rudders, tanks and moving masses may be included in the calculations. Typical situations considered are:

 

vertical and transverse accelerations at specified locations

roll and pitch motions

slamming, and green water on deck

risk of propeller/waterjet emersion

overall hydrodynamic analyses

 

Such analyses will answer questions about:

 

best and worst loading conditions?

critical speeds and headings?

wave height limitations?

likely levels of seasickness?

limiting seakeeping qualities?

percentage of time operable?

 

 

Wave-induced loads, local slamming loads

 

Global dynamic loads are caused by:

 

pressure forces due to waves and motions

inertial forces due to ship motion

restoring forces due to the motions relative to waves

 

 

Motions of the ship in rough weather can lead to structural problems

 

Our calculations can provide answers about:

 

bottom or bow slamming

water on the foredeck

bending, torsion, shear and fatigue failures

 

 

Direct computations

 

Loads from these analyses can be used in structural analyses as an alternative to classification design values of global loads (shear forces, bending moments, torsional/pitch moments), and can also indicate potential problem areas.

 

 

Structural analysis - fatigue and ultimate limit states from seakeeping analyses

 

The results from the hydrodynamic calculations may be used to calculate:

 

long-term distribution of stresses at specified locations

fatigue damage at specified locations

stress distributions within the ship structure at critical positions in design waves

local stress distribution during a slamming impact

 

Either of the following different approaches may be used, with improving accuracy:

 

combining global loads at ship cross sections

applying pressures and inertia forces to a 3D

finite-element model modal analysis

 

Long-term statistical results are obtained by postprocessing transfer functions from the vessel response calculations. This predicts possible fatigue damage, and estimates yielding, tearing and buckling capacities.

   

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