As the size of cruise ships has grown,
outbound transits, in particular during stronger winds, generate surge effects
within the harbor that have proven problematic for vessels at berth. As part of
the Canaveral Harbor Integrated Section 203 Navigation Study sponsored by the
Canaveral Port Authority (CPA), vessel-induced surge modeling was performed to
provide an assessment of passing vessel hydrodynamic effects and forces on
berthed vessels within the port, and potential changes following the proposed
channel widening and deepening project. The analysis evaluated potential
hydrodynamic changes on a port-wide scale and changes in loads on berthed
vessels.
Vessel-induced surge modeling was performed
according to scenarios developed collaboratively and coordinated among the CPA,
their project engineering consultants, the Canaveral Pilots, the local US Coast
Guard and the “Mission Partners,” which collectively refers to the Cape
Canaveral Air Force Station (CCAFS), Naval Ordinance Test Unit (NOTU), and the
Military Sealift Command (MSC). Modeling scenarios consist of different port
configurations, berthed vessel configurations, and passing ship scenarios. Two
port configurations were considered: Existing Conditions and Recommended Plan
(channel deepening and widening). The scenarios included 16 berths of interest
and five berthed vessel configurations (A-E) among Mission Partner and
commercial wharf and pier facilities. Passing ship scenarios consisted of
unique maneuvering schemes for each of the two port configurations, as well
south or north wind conditions.
Port Configurations
Canaveral Harbor is a complex water body, with
three main basins located off the main channel. Berths operated by the Mission
Partners and the CPA are located within the basins and along the north and
south sides of the main channel. Waterfront structures primarily include
open-piled piers, wharves, steel sheetpile bulkheads, submerged sheetpile
toewalls, ro/ro ramps, and pre-cast concrete pile or steel monopile mooring and
breasting dolphins. CPA commercial terminals largely serve cargo, bulk and
break-bulk carrier, tanker, and cruise operations.
Individual berths were described using known
dimensions and locations of surface-piercing bulkheads, submerged toe walls,
under-pier and berth box back slopes, and other features provided in the design
drawings. The Recommended Plan modeling domain was developed based upon the
widened and deepened navigation project features, adjacent slopes and new
berths, as well as bulkheads in the case of West Basin future improvements.
Design Vessels
Design vessel data and hull geometry were
provided, including type, class, name and particulars of all passing and
berthed vessels. The Mission Partners supplied hull data in various formats,
including vessel lines drawings, section and frame geometric descriptions and
three-dimensional CAD drawings. Some CAD drawings were complete with
superstructure geometry, whereas some commercial vessel hull models were
generated using scaled versions of hull forms from existing databases.
Passing Vessel Configurations
Three design passing vessels and their
maneuvering characteristics were selected prior to the analysis. The three
cruise ships included Carnival’s Fantasy Class (Fantasy), Royal Caribbean’s
Freedom Class (Freedom), and Disney’s Dream Class (Dream). On specific days of
the week, cruise ship outbound transits occur successively within a relatively
short period of time, and on some occasions have proven problematic for ships
at berth. Each ship’s conning position, distance north or south of the existing
or recommended project channel centerline, speed and drift angle were defined
for either northerly or southerly wind conditions. These variables were all
prescribed at six locations along the main channel. The modeling simulated
three cruise ships maneuvered in succession, beginning with Fantasy, Freedom
and Dream at 15-minute departure intervals. This is a typical weekend afternoon
succession of vessel maneuvering activity at Port Canaveral with events as
described in detail by the local pilots.
Existing Conditions
Surge Modeling
Passing vessel hydrodynamics were calculated
using the Vessel Hydrodynamics Longwave Unsteady (VH-LU) model (Fenical et al.,
2006). The VH-LU model predicts water level and velocity fluctuations
surrounding the passing ships and in all areas of the harbor. The model has
been thoroughly validated using a wide array of field and laboratory
hydrodynamic and berthed vessel loading measurements (Fenical et al., 2011) for
a number of previous marine engineering projects. Field validations have
included successful comparisons with measured water levels and velocities, and
validations with laboratory measurements have included successful comparisons
of water levels, velocities and forces on berthed vessels.
Qualitative Model Validation
The quantitative validation of the numerical
model via other project locations and field and laboratory measurements was
accepted by the CPA project team as applicable for the Port Canaveral modeling
in order to demonstrate the relative difference in large-scale, port-wide,
passing ship effects between the existing and recommended port plans. Therefore
no field measurements were collected on the project for model validation.
Qualitative validation was performed using Canaveral Pilot site observations
for several terminals and personal experience while conducting vessel movements
in the harbor.
Four primary site observations were reported
and reproduced in the model.
1) South Cargo Pier 4 (SCP4) - some of the
strongest surge effects have been experienced here - a typical parallel-passing
situation. The navigation area becomes more confined moving east of SCP4,
starting with the solid bulkhead at SCP3, resulting in an increased pressure
field intensity and surge (longitudinal) force at SCP4 in the model. This is
observed in the modeling results.
2) Trident Wharf - experiences surge effects,
passing speeds 7.5kts or greater generally cause issues. Since Trident Wharf is
far from the channel, surge amplification must be demonstrated in the modeling
to reproduce known impacts. The modeling results clearly reproducethe surge
amplification. The pressure field wave reflects against the north end of
Trident Basin, and produces a draw-down at that location with pressure field
intensity similar to that immediately adjacent to the passing vessel.
3) North Cargo Pier 2 (NCP2) - Surge issues
are not significant when passing vessels go by, but berthed ship motions occur
10-15 minutes later (time lag depending on passing vessel speed), even for a
single passing ship. To illustrate this, additional simulation for Existing
Conditions was performed using the Dream as a single passing vessel. The single
passing ship simulation predicted that a pressure field wave is generated at
the stern of Dream as it leaves the confined water of the Inner Reach. This
effect is generally observed where passing vessel pressure fields interact with
the transition between a narrow waterway and open water. Then, the pressure
field wave arrives at NCP2, approximately 11.5 minutes after Dream originally
passed the berth, which is within the 10-15 minute observation. Observation 3
is reproduced in the modeling results.
4) North Jetty Area - just inside the north
jetty is a wide, shallow sloping shelf, which is an observed area of water
level retreat and pressure field wave breaking. The model predicts that as the
pressure field wave approaches the shallows, the water retreats away from the
shoreline. As the pressure field wave moves into the shallows, it grows in
height and breaks, and moves north until impacting the jetty.
The accurate reproduction of these complex
physical processes reported from site experience provides a high level of
confidence in the modeling results and conclusions regarding the potential
mooring impacts associated with the proposed deepening/widening project.
Surge Changes from Channel Improvements
Passing vessel hydrodynamics were generated
for the recommended plan conditions in a manner consistent with modeling for
existing conditions. In general, pressure field intensity is reduced surrounding
the passing cruise ship due to the wider and deeper channel. In some areas, the
deepening alters the timing of the fluctuations. Water level fluctuations
inside the harbor are highly variable and strongly depend on the location of
interest.
Time histories were taken at all Mission
Partner and commercial berths, and water level fluctuations are generally
reduced at all berths of interest following channel improvements. In order to
characterize the surge changes on a spatially complete port-wide scale, exhibits
were generated for two parameters: maximum water level and maximum surge wave
height.
Following harbor improvements, particularly in
the narrow channel areas, and near Poseidon Wharf and the north end of Trident
basin, modeling showed a reduction in both the maximum water surface elevations
and the maximum surge height throughout the harbor, with a similar magnitude of
the reduction for the two different wind and sailing conditions evaluated.
Loads on Berthed Vessels
The VH-LU modeling system also computed the
hydrodynamic loads on the berthed vessels. The results of the hydrodynamic
analysis include vessel specific time histories of surge force, sway force, and
yaw moment for each of the modeling scenarios. Loads were calculated for those
berthed vessels of interest as specified within the Surge Modeling Plan and at
the time frame spanning the passing of the third and final outbound ship, the
Dream. Changes in loads on the ships were largely analogous to changes in water
level fluctuations introduced by the channel improvements. The vast majority of
the berthed ships experienced reduced peak surge and sway forces for
Recommended Plan modeling, with the timing of the forces altered as compared to
the Existing Conditions modeling.
Vessel hydrodynamic analyses were performed on
a port-wide scale, to evaluate future harbor surge and mooring conditions at 16
distinct terminals within Port Canaveral, Florida, for a series of three cruise
ships departing in succession. The hydrodynamic analyses utilized passing
vessel hydrodynamics and berthed vessel forces calculated using the VH-LU
vessel hydrodynamic modeling system. A total of 24 different hull models were
constructed, including 10 unique Mission Partner hull models and 14 commercial vessel
hull models.
The Recommended Plan channel improvements
result in a reduction in the intensity of pressure fields generated by the
passing cruise ships. Water level fluctuations are reduced throughout the
harbor, both in terms of maximum water level and maximum surge wave height. The
Recommended Plan channel improvements result in a general reduction in the
forces and moments on the berthed vessels, ranging from negligible to
approximately 35 percent as compared to Existing Conditions. Immediate
practical recommendations offered included an increase in the time between
successive cruise ship departures .
