The full story
Changing operational conditions
Bulk Terminal Wilhelmshaven mainly handles coal for nearby power plants, but is also used for the transfer of coal from ocean-going vessels to shallow draft vessels. While the outer jetty can host ocean-going vessels, the inner jetty is intended for use on a regular basis for shallow draft vessels. A statistical review of the terminal design – taking recent conditions into consideration – revealed that there was insufficient information to determine if the terminal could house two simultaneously-moored vessels.
Changing flow pattern
Due to the construction of the Jade Weser Port near the bulk terminal, modifications to the terminal itself became necessary. Both constructions resulted in a different flow pattern, leading to different loads in fenders and bollards compared to situations which were investigated in previous studies.
Impact of passing vessels
The impact of vessels navigating into the Jade Bight, a bay on the North Sea coast of Germany, was completely unknown. When a vessel moves through water, it creates a setup at the bow and setdown along the length of the vessel. This drawdown wave extends perpendicularly to the vessel and can intercept a moored vessel at an adjacent berth. The results of past studies, for instance, at the river Elbe, could not serve as a point of reference due to differences in passing distance, vessel type, size and speed.
Sophisticated numerical modelling
Using the latest technology in mooring analyses and hydrodynamic modelling, we carried out the following tasks that addressed the client’s concerns:
- Review of existing reports and data
Latest measurements of wind and hydrodynamics, as well as fender characteristics, were considered. This investigation revealed that information on passing vessels were limited. DHI collaborated with Nautisches Büro Bremen (NBB) on a regular basis to analyse existing vessel traffic data to clearly identify the characteristics of passing vessels.
- Calculation of drawdown waves due to passing vessel
The drawdown wave period is usually longer than wind wave periods, resulting in excitations which are closer to the Eigen frequencies of the moored vessels. Therefore, drawdown waves with small amplitudes can also result in large vessel motions. The passing vessel was simulated in a hydrodynamic MIKE 21 HD FM model. The resulting wave field served as an input condition for the mooring analysis. The vessel was implemented as locally-increased pressure field on a very fine mesh. In this way, the water was displaced as stencil, resembling the hull of a passing vessel.
- Dynamic mooring analysis for two simultaneously-berthed vessels
The vessel-induced drawdown wave, wind waves from northeast, tidal currents and wind from westerly directions were included to form the environmental conditions acting on the moored vessels. Both vessels were included simultaneously in the mooring setup. Different vessel orientations were also investigated.
Our team tested four mooring arrangements under several environmental conditions and came to these conclusions:
Insignificant passing vessel impact
The drawdown wave of vessels sailing into and from the Jade Bight resulted in small amplitudes, which were too small to cause dangerous situations during the loading and unloading of moored vessels.
Uncompromised safety of the bulk terminal
We determined that the flow pattern, which has been altered due to the construction of the Jade Weser Port and modifications to the bulk terminal, did not lead to reduced safety. This holds true even for situations where two vessels are berthed simultaneously.
Due to the number of different environmental conditions, recommendations for more efficient mooring arrangements were provided.