A Current can be added to the Hydrodynamic Response system to supplement the wave forces being applied to the structure. Current loading will be applied to tubular beams and slender tube elements using the velocities at the depth of the element. If cable dynamics is used for the definition of a composite catenary cable, current loading will also be applied along the length of the cable using the variable current velocity with depth.
Current loading is also applied at the center of gravity of a vessel (as long as Current Force Coefficients have been provided) and will utilize the current velocity at a specified Current Calculation Position, as defined in the Part details. Alternatively, where Morison Hull Drag Coefficients have been defined, current loads in a Hydrodynamic Response analysis are calculated using the current velocity at the depth of the structure center of gravity.
Note: Although you can add multiple Current objects to your analysis, you may only have one active Current; the others must be suppressed.
To add a Current:
Select the Hydrodynamic Response object in the tree view.
Right-click on the Hydrodynamic Response object and select Insert > Current >
Current Type, or click on the Current icon in the Analysis toolbar and select the current type from the dropdown menu.Click on the Current object in the tree and enter the current data.
Note: If an Irregular Wave is defined by importing a User Time History of wave elevations from a WHT file, it may be necessary to define the current profile with negative velocities: the WHT file must contain a positive constant current in order for the waves to be calculated correctly. The total current velocity will be the sum of the value in the WHT file and the values defined here.
For all types of Current it is necessary to define a Water Depth to which the current profile extends. By default, the Water Depth Definition is set to Use Water Depth in Environment Constants, and the Water Depth field will reflect the value defined under Details of Geometry; or, where a Composite Cable Seabed is defined, the Water Depth Definition may be set to Use Composite Cable Seabed Water Depth at Reference Point. Alternatively, the Water Depth Definition can be set to Manual Definition and the total Water Depth for the current profile can be entered directly.
Use the Type option to select the type of current that you would like to define. The following current types are available:
A Constant Velocity current does not vary with depth, and requires only its Speed and Direction to be defined. Both of these properties can be parameterized as part of a design point study.
In a more realistic description of the simulated environment the current definition should account for the variation of speed and direction with depth. When the current Type is set to Varies with Depth, Dimensional, this data can be entered directly into the Current Definition Data table.
Current depth is measured from the sea surface. The rows of the Current Definition Data table are automatically sorted in order of Depth from the sea surface to the sea bed.
Duplicate Depth entries, negative entries, or entries greater than the Water Depth are not valid. A maximum of 25 rows may be added. If a complete definition of current with depth is not defined between the water surface and the defined Water Depth, constant values will be assumed based upon the lowest and highest defined data.
Current Definition Data can be entered manually, can be copied and pasted from an external source (for example, an Excel spreadsheet), or can be imported from a comma-separated values (.CSV) file using the Import CSV File option. For the Import CSV File option, the file must meet the following requirements:
Has the .CSV extension.
Contains values separated by commas, tabs, or single spaces (not multiple spaces).
Contains exactly 3 columns, and no more than 25 rows.
The unit system of the data in the .CSV file is assumed to match the display unit system of the project. However, the imported data can be modified by setting the Length Unit for Imported Data and Rotation Unit for Imported Data to the required unit system.
When the current Type is set to Varies with Depth, Non-Dimensional, data can be entered as factors and offsets into the Current Definition Data table. Depth Factors are multiplied by the Water Depth; Speed Factors are multiplied by the defined current Speed; and Direction Offsets (which may be negative) are added to the defined current Direction. Current Speed and Direction can both be parameterized as part of a design point study.
Duplicate Depth Factor entries, negative entries, or entries greater than 1.0 are not valid. A maximum of 25 rows may be added. If a complete definition of current with depth is not defined between the water surface and the defined Water Depth, constant values will be assumed based upon the lowest and highest defined data.
Current Definition Data can be entered manually, can be copied and pasted from an external source (for example, an Excel spreadsheet), or can be imported from a .CSV file using the Import CSV File option. For the Import CSV File option, the file must meet the following requirements:
Has the .CSV extension.
Contains values separated by commas, tabs, or single spaces (not multiple spaces).
Contains exactly 3 columns, and no more than 25 rows.
The unit system of the data in the .CSV file is assumed to match the display unit system of the project. However, the imported data can be modified by setting the Rotation Unit for Imported Data to the required unit system.
In cases where it is impractical to measure current velocities at depth, you can use a Formulated current.
To represent a current generated by the tide, you can define a Tidal
Speed at the water surface, a Tidal Direction at the water
surface, and a Tidal Variation Inverse Exponent. The variation of current
velocity 
with increasing depth 
due to a tide is determined as
Where 
is the tidal speed at the water surface and 
is the total water depth. By default the Tidal Variation Inverse
Exponent will be set to 7, which yields a one-seventh power law profile (the
classic approximation for a fully-developed turbulent flow over a smooth solid
boundary).
To represent a current generated by the wind, you can define a Mean Wind
Speed and Mean Wind Direction (as measured over 1 hour at a
height of 10 meters), a Reference Depth, and a Wind Speed
Factor. The variation of current velocity 
with increasing depth 
due to a wind is determined as
Where 
is the reference depth, and 
is the wind-generated current speed at the water surface defined by
In which 
is the wind speed factor and 
is the mean wind speed measured over 1 hour at a height of 10 meters. The
Reference Depth has a default value of 50 meters, and the Wind
Speed Factor should typically lie within the range of 0.015 - 0.03.
Tide and wind-generated currents can be combined by defining parameters for both. The
total current velocity 
with increasing depth 
due to tide and wind is then
All properties of a Formulated current may be parameterized as part of a design point study; however, at least one of Tidal Speed and Mean Wind Speed must always be non-zero.
The Current Definition Data table will display the current profile which is generated from the input data. Use the Export CSV File option if you would like to save this data in the .CSV file format.
For each current depth, an arrow is drawn to represent the current direction and speed; these will be purple if valid, or yellow if invalid. For a Constant Velocity current, a single arrow is shown at the water surface. The arrows are scaled with speed, while the overall current profile is illustrated by the purple shaded region.
