The General HydroStatics SeaKeeping Module "SK" is designed to provide the GHS user with an integrated, general-purpose solution for seakeeping and hydrodynamic analyses. SeaKeeping is the result of significant in-house development work, and while it offers many features that may be found in other motions codes, it is also unique in many respects. Integration within the GHS environment also means calculations may be performed using existing geometry files, loading conditions, and run files. This translates to minimal additional user input, unmatched flexibility in its market segment, and ease of use.
SeaKeeping offers an excellent and economical solution for seakeeping and hydrodynamic analysis that is well suited to many applications. Some of the more common use-cases include:
- Motion Studies: Compute 6-DOF RAOs, statistics, periods and amplitudes, with or without forward speed in long-crested or short-crested seas.
- Cargo, Rigging, and Sea-Fastenings: Forecast accelerations at rigging and fastening points, supporting the calculation of rigging loads, design of cargo fastening systems, and cargo shifting.
- Habitability: Estimate periods, accelerations, and MSI encountered under way in a variety of sea ways to ensure crew comfort and safety.
- Crane Operations: Estimate absolute and relative responses at crane booms and lift points and accelerations at crane bases.
The module offers users the following features:
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- Integration with GHS command language and run files allows unmatched flexibility
- Included Seakeeping Wizard for GUI-driven analyses makes setting up complex seakeeping runs quick and easy
- Available Acceleration Transform Wizard makes it easy to compute deck-parallel and deck-normal acceleration components (with or without the gravitational acceleration term) for cargo and sea-fastening applications
- Use of GHS geometry files (.GF) for seakeeping analysis eliminates the need to create additional models
- Minimal input and ease of use compared to other commercial codes
- Recognizes vessel loading condition as specified in GHS, meaning all tank weights, added weights, and lightship distributions are automatically included and there is no need to specify hydrostatic parameters, what is needed is accessed directly
- Full support for monohull vessels
- 6-DOF motions including displacements, velocities, accelerations, amplitudes and phase angles
- Absolute and relative motions
- Motions may be computed at the vessel center-of-gravity and at specified Critical Points
- Critical Points responses are point-specific, and automatically include any coupling effects (such as pitch-into-heave effects near the bow of a pitching vessel) so there is no need to perform these tedious calculations, the results are direct
- Response amplitude operators (RAOs) for all DOF at CG and/or any Critical Point are automatically computed
- Statistical response data including variance (m0,m2,m4), RMS, average and significant response amplitudes, average periods, and extreme maxima are automatically computed when using wave spectra
- Accelerations may be given in Ft/Sec2, m/Sec2, or gravitational units "g's"
- User specified confidence limits and time intervals allows for custom definition of extreme response amplitudes
- Optional overall or case-specific summary tables include extreme position, velocity, and/or acceleration amplitudes for the CG and/or all Critical Points offering an ideal "one-location" reference table for design values
- Easily compute the maximum response(s) for the CG and/or all Critical Points over a range of headings and/or speeds
- The ability to analyze vessels with non-zero heel and/or trim means realistic loading conditions can actually be evaluated
- Robust geometry handling alerts the user to potential issues
- Unique trapped-water method offers first-order approach for stern ramps, well decks, and other unusual spaces
- Optional full-coupling, partial-coupling, or full-uncoupling of the equation of motion
- Optionally compute all 36 hydrodynamic added mass and damping coefficients
- Robust linear, rigid-body, frequency domain, advanced strip-theory formulation includes the following theoretical enhancements:
- Computes exact 3D normal vectors using a 3D triangular mesh, does not use 2D or slender-body normal vector approximations, yielding more accurate solutions, and greatly improved solution convergence when increasing the density of sections
- Includes a more complete treatment of speed corrections in forces and coefficients for better forward speed approximations
- Makes no symmetry assumptions
- Boundary element method (2D Rankine panel method) solves the radiation problem directly for each section and can accommodate most ship geometry, incl. anti-symmetric geometric sections (i.e. non-zero heel), fully-submerged sections, and partially submerged sections
- Computes the diffraction potential for all modes using the Haskind relations, yielding robust diffraction forcing solutions with reduced computation time
- Offers a fully-coupled hydrodynamic added mass and damping matrix, meaning all 36 coefficients may be computed
- Offers a generalized mass matrix including all physical mass and mass-moment terms and a fully-defined inertia tensor that interfaces automatically with the current loading condition
- Offers a generalized hydrostatic stiffness matrix including all restoring terms
- Advanced parameterization of hydrodynamic 2D panel mesh
- Long-crested waves at any wave heading
- Short-crested waves using spreading functions via the Seakeeping Wizard
- Regular or irregular waves at any wave heading
- Single wave or wave spectra input (via WAVE command extension)
- Available wave spectra include:
- Bretschneider (General, Narrow-band, and ITTC 1984)
- JONSWAP (general form)
- JONSWAP (ITTC 1978)
- Ochi-Hubble (6-parameter)
- Ochi-Hubble (most probable, single-parameter via Hs)
- User data file
- Two parameterized wave spectra sampling methods (constant variance or evenly sampled frequency range) for seaway discretization
- Non-zero vessel speed at any wave heading
- Easily run individual or multiple wave headings within a single command
- Easily run one or more forward speeds within a single command
- Slamming probabilities, frequencies, and estimated pressures may be computed at a specific location or at frame locations using a frame file
- Deck submergence "Shipping Water" probabilities and frequencies may be computed at a specific location or at all Critical Points
- Motion Sickness Incidence (MSI) with variable exposure period may be computed at a specific location or at all Critical Points
- Automated polar plotting for multiple headings enables easy generation of polar plots for any response statistic (RMS, Extreme, etc.), and/or derived responses
- Six (6) optional comma-separated output data files:
- Response Data: includes RAOs and phase angles for all modes and all Critical Points
- Forcing Data: includes total, inertial, and diffraction wave excitation forcing amplitudes per unit wave amplitude and phase angles
- Hydrodynamics Data: includes hydrodynamic and hydrostatic coefficients (i.e. A, B, and C's)
- Wave Data: includes wave sample characteristics such as periods, frequencies, spectral ordinate, sample amplitudes, etc.
- Variance Data: includes response variance (m0, m2, m4) for all modes and all Critical Points
- Statistics Data: includes response statistics such as periods, RMS, average, significant, and extreme amplitudes
- Full-featured and comprehensive report file includes all RAO and phase angle tables and plots, response statistics, continuous and sampled spectra tables and plots, summary tables, derived response tables, and polar plots
Contact Customer Support
to inquire about current and prospective feature updates. SeaKeeping is always being updated and improved.
Seakeeping calculations create a lot of data, which is both a necessity and a curse when you are trying to review results. Seakeeping output is designed to make it as easy as possible to reference specific RAOs or response results for certain Critical Points or heading/speed combinations (a.k.a. Cases) without omitting important supporting information. SeaKeeping reports are organized according to the following structure, with options to include or omit various sections:
- INPUT SUMMARY
Summary of general input parameters, including method type, geometry component, and meshing parameters.
- CRITICAL POINTS
Table of user specified Critical Points, overall vessel CG, and any optional derived response points (SHW, MSI).
Case number, case-specific wave heading and ship speed
- Wave Components
Summary of overall wave/spectra type, wave samples, and sampling method parameters. Also includes tabulated wave period, frequency, LWL/WvLen, encounter frequency, ordinate, and amplitude for each wave component.
- RAOs and Phase Angles (Position, Velocity, and/or Acceleration)
Tabulated RAOs and phase angles for all modes for each Critical Point. Also includes a plot for each mode, with results for all Critical Points plotted together.
- Response Statistics (Position, Velocity, and/or Acceleration)
Tabulated response statistics for all modes for each Critical Point. Includes variance (m0, m2, m4), average periods (ZUC/Maxima), RMS, average, significant, average maxima, and optional confidence/interval extreme amplitudes.
- Derived Responses (Optional)
- Deck Submergence/Shipping Water "SHW"
- Motion Sickness Incidence "MSI"
- Case Summary Table (Optional)
Table of user requested absolute response amplitudes for all modes for each Critical Point. Displays the response for the preceding case.
- OVERALL SUMMARY TABLE (Optional)
Table of overall user requested absolute response amplitudes for all modes for each Critical Point. Displays the maximum over all cases.
To help parse especially large runs, SeaKeeping offers optional case-specific or overall summary tables which display user requested position, velocity, and/or acceleration amplitude components in the x (Surge), y (Sway), z (Heave) translational directions, and the X (Roll), Y (Pitch), Z (Yaw) angular directions. These tables are an ideal "one-location" reference point for design values or initial review, and are always located at the end of each reported case.
In addition to comprehensive reports, SeaKeeping offers six (6) optional comma-separated-variable (CSV) data files that may include any of the information found in the report in a convenient form for input into spreadsheets, third-party programs, or further post-processing by run-files.
SeaKeeping reports include an initial section that summarizes input parameters, condition information, and specified Critical Points. A wave component summary table is also included, and if wave spectra are used, a wave spectra plot is included that shows both the continuous wave spectrum and the discrete wave samples used by SeaKeeping. Optional derived responses are then appended to the end of each case.
Get Access to a Trial Version
If you are interested in testing the SeaKeeping Module, contact sales
to inquire about a temporary license. We will work with you to set up a trial period that meets your evaluation needs.
A number of core validation studies, including coefficients, forcing, RAOs, relative motions, and accelerations, may be found here.