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Data: Calculation and output |
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Data: Calculation and output |
OrcaWave offers the following solve types:
OrcaWave always solves the potential formulation. The solution yields results for the velocity potential, $\phi$, at all mesh panels. This enables pressure to be evaluated on the surface of all bodies, and hence results include added mass and damping, load RAOs and displacement RAOs.
Solving the source formulation yields results for the source function, $\sigma$, at all mesh panels. This enables tangential fluid velocity to be evaluated on the surface of all bodies, and hence additional results are available including panel velocity and mean drift loads using the pressure integration method.
In addition to solving the potential and source formulations for each first-order frequency, OrcaWave will also solve for the second-order potential at second-order frequencies. Results are generated for the potential loads and the quadratic loads, which together give the full QTFs.
OrcaWave can compute load RAOs using either the Haskind relations, or the diffraction load formula, or both. If both types of load RAO are computed, then the preferred load RAO calculation method will determine which load RAOs are used in the calculation of displacement RAOs, and also it will set the default choice for which load RAO data to import when importing results into OrcaFlex (you can change your mind at the import stage).
Quadratic loads include mean drift loads and, when a full QTF calculation is performed, time-varying quadratic loads. OrcaWave offers three calculation methods: pressure integration, control surface integration and momentum conservation. The preferred quadratic load calculation method will set the default choice for which quadratic loads to import when importing results into OrcaFlex (you can change your mind at the import stage).
| Note: | Momentum conservation cannot be the preferred method in multibody or full QTF models, due to the limitations of that method. |
This option allows you to include a damping lid on the free surface. A damping lid can be used to damp resonant responses in the fluid, e.g. in a confined space such as a moonpool or a narrow gap between vessels. A damping lid cannot be included when a full QTF calculation is performed.
These tolerances are used in the diffraction calculation. Their values may affect results. They are also used for the validation of input data.
The length tolerance is used to determine whether two points are equal or whether a point lies in a plane. For example, OrcaWave will classify a panel as being on the free surface if $|Z_C|$ is less than the length tolerance, where $Z_C$ is the vertical component of its centroid. Ideally, a free-surface panel would have $Z_C=0$ exactly. The length tolerance allows some leeway, but it should always be as small as possible.
The waterline Z tolerance is used to classify whether a vertex of a body panel forms part of a body waterline, $\CWL$. OrcaWave will classify a vertex as part of a waterline if the magnitude of its $Z$ component is less than the waterline Z tolerance.
| Note: | Ideally, panel vertices that are part of a waterline should have a $Z$ coordinate of exactly 0. The waterline Z tolerance allows some leeway if this is not the case. |
The waterline gap tolerance is used to determine whether two segments on a body waterline, $\CWL$, are connected.
| Tip: | The waterline Z tolerance and waterline gap tolerance should usually be larger than the length tolerance, to allow for small errors and adjustments that are often present in panel data. |
When this option is selected OrcaWave will divide any non-planar quadrilateral panels into two triangular panels. A panel is considered to be non-planar if its projection length exceeds the length tolerance.
If the momentum conservation quadratic load method is included in the calculation, this data determines the number of quadrature nodes for the integration of the Kochin functions with respect to $\theta$.
Diffraction calculations rely on the solution of linear matrix equations of the form $A\vec{x} = \vec{b}$, where $\vec{x}$ is unknown. OrcaWave offers two solution methods:
In broad terms, the direct solver is faster for smaller meshes, and the iterative solver faster for larger meshes. A secondary factor that impacts performance is the number of headings. The direct solver can solve for multiple headings without performing much extra work beyond what is needed for a single heading. However, for iterative solvers the total work is proportional to the number of headings.
The iterative solver uses the accelerated Gauss-Seidel method described in Lee 1988.
As a general guideline, we would typically recommend using the direct solver. Whilst the iterative solver is faster for large meshes, it is our experience that the mesh needs to be huge in order for the iterative solver to be faster. Such huge meshes are rare, and present other problems, notably with memory consumption.
The diagnostics sheet of the results tables reports timing information to help guide your choice.
The maximum number of iterations that can be attempted before the solver fails. In the event of the iterative solver failing to find a converged solution, OrcaWave will fall back to use the direct solver.
The solution tolerance, $\epsilon$, for the iterative solver. The iteration is deemed to have converged when $\| A\vec{x} - \vec{b} \| \leq \epsilon \| b \|$.
These options allow you to decide whether to include certain quantities in the OrcaWave results:
| Note: | Panel results and intermediate results can significantly increase the size of an OrcaWave results file. |
These options do not affect calculation results. They are only used in the validation of input data.
When this option is selected OrcaWave will perform additional validation checks including checking for overlaps or gaps between panels. If selected, three additional warning levels become active.
| Tip: | Validation of panel arrangement takes longer to complete than the validation of individual panels because it involves a loop over all pairs of panels. If your mesh is large you may want to perform this validation once and then uncheck this box. |
These values determine the thresholds for various warning messages during validation of input data.