Part C | 31.3
706 Part C Coastal Design
in which, the retardation function
R kj .t/ D
2
1
Z
0
B kj .!/ cos.!t/ d! ;
where:
! D the wave frequency (rad/sec)
m kj D vessel-frequency-independent added mass
coefficient matrix and can be obtained from the following equation
m kj D A kj .!
0
/ C
1
! 0
R 1
0 R kj .t/ sin.!
0 t/ dt
!
0
D an arbitrarily chosen value of !. The result for
m kj is independent of the value of !
0 A kj .!
0
/ and is
the frequency-dependent added mass of vessel.
The set of vessel motion equations in time domain
can be solved for x j for each time step, and the corresponding mooring loads can be obtained from the
known load-elongation curve for the mooring line or
the load-excursion curve for the chain and anchor, or
the reaction-deflection curve for the fender (if applicable). The wave forces (first order of wave load, the mean
drift wave force, and oscillating drift wave force) can be
computed though utilizing the corresponding vessel hydrodynamic database.
Commercially available programs have been developed for mooring analysis both by static and dynamic methods. These include [31.21] for static analysis, [31.22] for a time-domain dynamic method,
and [31.23] for both frequency and time-domain dynamic models.
Depending on site-specific conditions (metocean,
type, and size of vessel, and mooring layout) and the
project phase (feasibility study, conceptual design, preliminary design, or final design), and available budget,
the complexity of this analysis varies from very simple
hand calculations to complicated dynamic computeraided mooring models. For a vessel moored at a pier
or wharf, typical input data for a dynamic mooring analysis model include the vessel characteristics
(length overall, length between perpendiculars, beam,
loading condition, draft, vessel displacement, windage
areas, fairlead coordinates, mooring line properties,
winches/bollard capacity), basin water depth, metocean
conditions at berth, fender or dolphin locations and
properties, and safe working capacity of on-shore mooring fittings. The output of analysis includes mooring
loads and, if applicable to vessel unloading requirements, vessel responses in surge, sway, heave, roll,
pitch, and yaw. References [31.2], [31.16], [31.24] and
[31.25] can be used as references.
Vessel collisions with marine structures are rare and
infrequent but have occurred in the past. There are no
definitive standards or requirements for design for such
events, typically an errant barge, but occasionally for
a ship that has lost power. Coastal engineers may occasionally be required to recommend design requirements
that can typically be based on actual vessel traffic which
in the US is available through the US Coast Guard. The
authors of [31.26, Sect. 3.14] provides some guidance
for bridge structures, which can serve as guidelines for
marine structures.
31.3.3 Loads on Structures due to Ocean
Environmental Conditions
The load sources in the ocean environment include
wind, wave, current, tide and storm surge, ice, tsunamis
caused by earthquakes, and vessel propeller wash.
Among these load sources, for the majority of situation,
the wave load is the most complicated and the most important load that needs to be analyzed for the port and
harbor structure design.
Wind
Wind load could be critical in some cases. Strong
winds can be generated by hurricanes, typhoons, tropical storms, and locally generated storms. For port and
harbor design, long-term wind records are usually required to derive the extreme wind for different return
periods. When such records are not available, numerical
wind models are often employed. It needs to be realized that it is difficult to predict the wind with sufficient
accuracy with numerical models. Due to its dynamic
nature, the accurate calculation of wind load on marine
structures is difficult. In most situations, appropriate approaches are employed. Depending on the input of wind
to the formula or model, there are two methods commonly used for wind load calculation. The first method
for wind load calculation is to use constant speed. The
second method for it is to use constant wind speed plus
gusting wind. The commonly used wind spectrums for
wind gusting include API, Ochi-Shin, and Harris-DNV.
When performing the wind load calculations, it is important to apply the concept of wind duration. For rigid
marine structures, it is reasonable to use the 3 s gust,
as is used by most building codes. However, for the
vessel, a much longer wind duration needs to be used
for the wind load calculation. Depending on the size of
the vessel and corresponding anchor or mooring system, it could be of the range from 15 to 60 s. Many
references are available for wind load calculation, these
include [31.27–29], etc.
Waves
For port or harbor design, the wave prediction and wave
loads are a primary concerns for the designer. For many
706 Part C Coastal Design
in which, the retardation function
R kj .t/ D
2
1
Z
0
B kj .!/ cos.!t/ d! ;
where:
! D the wave frequency (rad/sec)
m kj D vessel-frequency-independent added mass
coefficient matrix and can be obtained from the following equation
m kj D A kj .!
0
/ C
1
! 0
R 1
0 R kj .t/ sin.!
0 t/ dt
!
0
D an arbitrarily chosen value of !. The result for
m kj is independent of the value of !
0 A kj .!
0
/ and is
the frequency-dependent added mass of vessel.
The set of vessel motion equations in time domain
can be solved for x j for each time step, and the corresponding mooring loads can be obtained from the
known load-elongation curve for the mooring line or
the load-excursion curve for the chain and anchor, or
the reaction-deflection curve for the fender (if applicable). The wave forces (first order of wave load, the mean
drift wave force, and oscillating drift wave force) can be
computed though utilizing the corresponding vessel hydrodynamic database.
Commercially available programs have been developed for mooring analysis both by static and dynamic methods. These include [31.21] for static analysis, [31.22] for a time-domain dynamic method,
and [31.23] for both frequency and time-domain dynamic models.
Depending on site-specific conditions (metocean,
type, and size of vessel, and mooring layout) and the
project phase (feasibility study, conceptual design, preliminary design, or final design), and available budget,
the complexity of this analysis varies from very simple
hand calculations to complicated dynamic computeraided mooring models. For a vessel moored at a pier
or wharf, typical input data for a dynamic mooring analysis model include the vessel characteristics
(length overall, length between perpendiculars, beam,
loading condition, draft, vessel displacement, windage
areas, fairlead coordinates, mooring line properties,
winches/bollard capacity), basin water depth, metocean
conditions at berth, fender or dolphin locations and
properties, and safe working capacity of on-shore mooring fittings. The output of analysis includes mooring
loads and, if applicable to vessel unloading requirements, vessel responses in surge, sway, heave, roll,
pitch, and yaw. References [31.2], [31.16], [31.24] and
[31.25] can be used as references.
Vessel collisions with marine structures are rare and
infrequent but have occurred in the past. There are no
definitive standards or requirements for design for such
events, typically an errant barge, but occasionally for
a ship that has lost power. Coastal engineers may occasionally be required to recommend design requirements
that can typically be based on actual vessel traffic which
in the US is available through the US Coast Guard. The
authors of [31.26, Sect. 3.14] provides some guidance
for bridge structures, which can serve as guidelines for
marine structures.
31.3.3 Loads on Structures due to Ocean
Environmental Conditions
The load sources in the ocean environment include
wind, wave, current, tide and storm surge, ice, tsunamis
caused by earthquakes, and vessel propeller wash.
Among these load sources, for the majority of situation,
the wave load is the most complicated and the most important load that needs to be analyzed for the port and
harbor structure design.
Wind
Wind load could be critical in some cases. Strong
winds can be generated by hurricanes, typhoons, tropical storms, and locally generated storms. For port and
harbor design, long-term wind records are usually required to derive the extreme wind for different return
periods. When such records are not available, numerical
wind models are often employed. It needs to be realized that it is difficult to predict the wind with sufficient
accuracy with numerical models. Due to its dynamic
nature, the accurate calculation of wind load on marine
structures is difficult. In most situations, appropriate approaches are employed. Depending on the input of wind
to the formula or model, there are two methods commonly used for wind load calculation. The first method
for wind load calculation is to use constant speed. The
second method for it is to use constant wind speed plus
gusting wind. The commonly used wind spectrums for
wind gusting include API, Ochi-Shin, and Harris-DNV.
When performing the wind load calculations, it is important to apply the concept of wind duration. For rigid
marine structures, it is reasonable to use the 3 s gust,
as is used by most building codes. However, for the
vessel, a much longer wind duration needs to be used
for the wind load calculation. Depending on the size of
the vessel and corresponding anchor or mooring system, it could be of the range from 15 to 60 s. Many
references are available for wind load calculation, these
include [31.27–29], etc.
Waves
For port or harbor design, the wave prediction and wave
loads are a primary concerns for the designer. For many