The Wave Frequencies tree object enables the definition of a range or single wave frequency to use in the analysis.
By default the frequency Range is Program Controlled; this equally spaces the specified Total Number of Frequencies between a minimum value based on the water depth (or the default minimum of 0.1 rad/s, whichever is larger) and a maximum based on the mesh size. The spacing interval can either be based on constant frequency or constant period increments (Intervals Based Upon, which also applies to any additional frequency range definitions).
You can manually define a single frequency or a range of frequencies by selecting Manual Definition for the Range. For a single frequency, set Definition Type to Single. Then set Lowest Frequency Definition to Manual Definition if you wish to edit the Lowest Frequency or Longest Period.
To specify a range of frequencies, set Definition Type to Range. Change Lowest Frequency Definition and/or Highest Frequency Definition to Manual Definition to edit the Lowest Frequency and Highest Frequency, or the Longest Period and Shortest Period, as required.
The Lowest Frequency will default to 0.1
rad/s and the Highest Frequency will default
to that determined by the mesh. The lowest wave frequency permitted
is calculated by 
rad/s,
where d is the water depth and g is the acceleration due to gravity.
The intermediate positions in a range are defined by entering a Number of Intermediate Values. The Interval Frequency or Interval Period will be updated automatically (according to whether Intervals Based Upon is set to Frequency or Period).
To specify additional frequencies, set Additional Range to Single or Range and enter the Period/Frequency and Number of Intermediate Values information. Any duplicate frequencies are automatically removed. The number of frequencies chosen extends the solution time linearly.
The Wave Frequencies table displays the frequencies and associated wavelengths of the waves that are included in the Hydrodynamic Diffraction analysis.
Note: To perform a subsequent Hydrodynamic Response analysis using Convolution, a Hydrodynamic Diffraction/Radiation analysis must be performed with at least 5 wave frequencies.
The frequency range must be wide enough to ensure an accurate calculation of the radiation force in the Hydrodynamic Response. For more information, see The FREQ/PERD/HRTZ Data Record - Frequencies/Periods at which the Hydrodynamic Parameters are Computed in the Aqwa Reference Manual.
If the Hydrodynamic Diffraction analysis is to be performed over a single Wave Direction with a Forward Speed defined, a table of the encounter frequencies in the analysis will be displayed in the Table tab of the Encounter Frequencies panel. The number of encounter frequencies will always be equal to the number of defined incident wave frequencies.
Clicking on the Graph tab of the Encounter Frequencies panel presents a graphical display of encounter frequencies against the corresponding incident wave frequencies. Negative encounter frequencies (which typically occur at higher incident wave frequencies/larger forward speeds) are permissible.
If the Hydrodynamic Diffraction analysis is to be performed over multiple Wave Directions with a Forward Speed defined, additional Encounter Frequencies Options are available. Set Encounter Frequencies (Target) as a guide value for the number of encounter frequencies. Following the rules described in The FWDS Data Record - Define Forward Speed, Aqwa will use this target to determine the number of Encounter Frequencies (Actual) that will be included in the Hydrodynamic Diffraction analysis. This will always be more than the number of defined incident wave frequencies.
The Display Encounter Frequencies option allows you to switch the information that is shown in the Encounter Frequencies panel. When Display Encounter Frequencies is set to For All Wave Frequencies and Directions, the Table tab will show the encounter frequencies corresponding to all combinations of incident wave frequencies and directions.
The Graph tab will show the same information as a 3-D surface plot:
When Display Encounter Frequencies is set to In Hydrodynamic Analysis Only, the Table tab will show the subset of encounter frequencies that Aqwa will choose to include in the hydrodynamic database. The Graph tab will show these encounter frequencies in ascending sequence order.
Note: Where the number of Encounter Frequencies (Actual) is less than the product of the number of incident wave frequencies and the number of defined wave directions, diffraction forces and potentials in the Hydrodynamic Diffraction analysis will be interpolated between the available data in the hydrodynamic database.
Aqwa will try to calculate over the whole range of encounter frequencies (both positive and negative) corresponding to the defined incident wave frequencies, wave directions, and forward speed. However, the minimum absolute encounter frequency is limited to 0.001 rad/s.