Mooring solutions for long waves & seiching

Mooring Solutions for
long waves & seiching

Dynamic Moored Vessel Analysis

OMC has extensive experience in modelling the motions of moored ships exposed to various environmental conditions, resulting in unparalleled expertise in mooring design and ship motion modelling. OMC developed the numerical model, SPMS (Simulation Package for the Motions of Ships), for the analysis of various problems associated with the motions of vessels, either moored, towed or free moving along channels or in deep water.

Since development commenced in 1962, it has been extended to solve a wide variety of maritime projects in Australia and overseas. This includes analysis of motions, line tensions and fender forces of bulk carriers, oil tankers, container vessels, frigates, submarines, Ro-Ro vessels, general cargo ships and tugs at a wide variety of berths, including spread moorings, swamp moorings, fendered jetties and single point moorings. The model has also been used for the analysis of the relative motions of a transhipment

The SPMS numerical model includes the capability to model the slow drift oscillations of moored vessels due to long waves (periods greater than 30 seconds), as well as the wave frequency oscillations caused by sea and swell waves. Long period waves can be the most important driving force on moored vessels exposed to ocean swell because they can excite large amplitude, low frequency oscillations of the moored vessel in the horizontal modes of surge, sway and yaw.

These oscillations occur at frequencies similar to the corresponding natural frequencies of the ship/ line/fender system, leading to possible resonance amplification of the moored vessel motions, breakage of mooring lines and damage to berth and fenders – unlike wave frequency motions which are relatively highly damped, low frequency motions are only lightly damped, hence the great danger of resonance amplification arising from any significant long wave excitation.

Major calibration and validation exercises for the SPMS moored ship model have been completed during 1998/99 for two vessels at Port Taranaki on the west coast of New Zealand, during 2005 for two vessels at Geraldton and in 2006 for three vessels at Port Hedland, Western Australia.

These exercises involved DGPS measurement of moored ship motions, direct measurement of line tensions by strain gauges and collection of short and long wave data at the berth. An important outcome of these studies was the full-scale calibration and validation of the low frequency damping forces generated by the SPMS model.

Full-Scale Validation

The DUKC® and its associated models have undergone more validation that any other UKC management system.

OMC has carried out close to 100 full scale measurement validation campaigns, comprising more than 600 vessels at 40 different locations globally. This includes all major vessel types with varying depth/draft ratios, stability characteristics and transit speeds, channel configurations, tidal patterns and wave climates.

This data is analysed to validate the numerical model predictions utilising the measured wave, current and tide data against the ship particulars, thereby verifying the vessel motions.

Validation campaigns have been performed for both underway vessels and moored vessel applications.

Vessel Interaction Expertise

OMC has extensive experience with passing vessel interactions, and was an Industry partner in the Marin Research Institute Research on Passing Effects on Ships (ROPES) research project.

ROPES was a joint industry project and included development and validation of a computer tool to predict the effect of passing vessels for existing and new port and terminal developments. The project included extensive scale model testing and full scale monitoring campaigns in the Port of Rotterdam. Participants in the project included Ports of Rotterdam, Antwerp and Amsterdam, ExxonMobil, Cavotec, KRVE, and Deltares. As a partner OMC holds and has full rights to the developed IP which has used to both validate the OMC passing vessel model and to complement it for ongoing projects.

OMC has undertaken passing vessel mooring studies at Fremantle (2017), Gladstone (2017, 2016), Port Hedland (2014, 2012, 2011, 2010, 2009, 2008, 2006) Newcastle (2011, 20106), Brisbane (2012), and Cape Lambert (2010). For these studies, OMC has used modelling to determine optimum vessel passing speeds and distances given the prevailing environmental conditions, tidal levels and characteristics of both the moored and passing vessels. The Port Hedland study also involved validation of the model against full scale measurements, with excellent correlation between measured data and model outputs.

Berth Warning System

In addition to mooring studies, OMC has also developed the Dynamic Berth Warning System (BWS) to improve port operating safety.

The BWS is a real-time berth warning system designed to provide assistance to terminal operators in making decisions as to the operating safety of berthed vessels. BWS assesses both the vessel motions and the loads placed on moorings, lines and fenders by ocean swells, currents, and wind to provide produce a rating of port operating safety.

The BWS can incorporate wind, wave, and current forecasts from the National Weather Service, or private forecast providers, giving the potential to provide dynamic berth operability forecasts up to a week in advance, improving berth safety and performance.