Hydrodynamic Diffraction analyses can take advantage of Parallel Processing with the proper licenses. For more information, see Setting Aqwa Parallel Processing Options.
The Generate Wave Pressures option specifies whether Aqwa should generate a Cartesian grid of wave pressures around the analyzed structures. This option must be set to Yes if you wish to include results in which the surrounding wave surface is displayed (Pressures and Motions results), or results which display the hydrodynamic pressures of fluids within Internal Tanks (Internal Tank Pressures results) .
When Generate Wave Pressures is set to Yes the following Wave Grid options are available:
Wave Grid Resolution allows you to double the resolution of the wave surface from 81 x 51 wave grid nodes (Standard) to 161 x 101 nodes (Fine). This is useful to capture the wave shapes of high-frequency wave components, particularly where encounter frequencies are increased due to a vessel’s forward speed.
Wave Grid Size Factor controls how much larger the sea area is than the structure (or structure group, if there are interacting structures present). The default value of 2 will cause the sea area to be twice as long as the structure in the X or Y directions, a ratio of X = 1.6 Y is maintained.
The following options are available to the Hydrodynamic Diffraction analysis system:
These analysis settings control how the analysis is performed. In normal circumstances they will not need adjusting. However, if you get modeling warnings then you may wish to turn on the Ignore Modeling Rule Violations option.
Note: Mean wave drift coefficients are always included in the Hydrodynamic Diffraction calculation. If you do not want to include drift forces in a subsequent Hydrodynamic Response analysis, you can achieve this by setting the Omit Calculation of Drift Forces to Yes in any Irregular Wave objects that have been added to the Hydrodynamic Response analysis. This option is only available for Irregular Wave Response with Slow Drift calculations.
- Ignore Modeling Rule Violations
If Yes, modeling rule violations will not stop the analysis. Most modeling errors generate warnings when this option is set to Yes. Do not use this option unless violations are minor and difficult to correct. For more information on modeling rules, see Mesh Quality Check in the Aqwa Theory Manual.
- Calculate Extreme Low/High Frequencies
If Yes, in addition to the frequencies defined in Wave Frequencies, the solver also calculates solutions at a 'very low' frequency and a 'very high' frequency. These are added to improve the calculation of the full QTF matrix in the Hydrodynamic Diffraction analysis, and to improve the convolution of radiation forces in any subsequent Hydrodynamic Response analyses.
This option must be turned on when the model includes active Moonpools. This enables the correct options in the solver file. Failure to do so will result in an error message, and the solve will be stopped.
- Include Multi-Directional Wave Interaction
If No, do not account for interactions between different wave directions in the calculation of QTF coefficients. Setting this option to No prevents the Apply Mean Drift Force with Multi-Directional Wave Interaction option from being used in any subsequent Hydrodynamic Response analysis.
- Near Field Solution
If Program Controlled, the far field solution is used in the calculation of mean drift forces where possible. However, the far field solution only calculates the mean drift force in three horizontal degrees of freedom (surge, sway, and yaw) and is unable to consider the hydrodynamic interaction between structures. For analyses in which the full QTF matrix is to be calculated or which contain multiple interacting structures, the near field solution must therefore be used.
If Yes, specifies that the near field solution should be used.
- Linearized Morison Drag
If Yes, computes linearized Morison drag for tube, disc, and slender tube elements. In order for the drag to be computed, after enabling Linearized Morison Drag an Irregular Wave must be added to the Hydrodynamic Diffraction analysis. Only one spectrum can be defined (no Irregular Wave Group). The Irregular Wave must have only a single direction defined (no Cross Swell).
This option will not be available if multiple structures are connected with a Connection Stiffness matrix. If set to Yes and a Connection Stiffness object is then defined between two structures it will show as a yellow field. In addition, the Analysis Options item will be marked with the question mark until either: the Connection Stiffness matrix is suppressed or is changed to connect between a point and a structure; or, the option is set to No.
The analysis settings control the use of the QTF matrix. For more information, see the Aqwa Reference Manual.
- Calculate Full QTF Matrix
If Yes, the program calculates the full QTF matrix.
These analysis settings control what is written to the Aqwa output text file or to specific additional files. For more information, see the Aqwa Reference Manual.
- Source Strengths
If Yes, writes the singularity strengths for both the modified and unmodified values to the *.LIS file, the modified strengths being a linear combination of the unmodified values. The actual relationship is a function of the number of body symmetries that are used.
- Potentials
If Yes, writes the modified and unmodified values of the potential at the diffraction element centers and at the field points to the *.LIS file. This information may be used to define the fluid flow field about the body.
- Centroid Pressures
If Yes, writes the hydrostatic differential and hydrodynamic fluid pressures at each plate in the model to the *.LIS file.
- Element Properties
If Yes, writes complete details of each element used in the body modeling to the *.LIS file. All important details of the body elements are output together with the resultant properties of the bodies.
- ASCII Hydrodynamic Database
If Yes, prints the hydrodynamic database (the .HYD file) in a compact ASCII format to a new file with a .AH1 extension. This option must be set to Yes in order to use the Output Example of Hydrodynamic Database option.
- Example of Hydrodynamic Database
If Yes, prints a sample of the .AH1 file, with annotation to explain the format.
- Generate AHD Pressure Output
If Yes, the program runs an additional post-processing step to write real and imaginary pressure components, over all wave frequencies and directions in the Hydrodynamic Diffraction analysis, to a new file with an .AHD extension. For analyses that include Morison elements, the disturbed wave kinematics at Line Body mesh nodes are also included.