SeaKeeping
GHS-SK Optional Module

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:
What Makes SeaKeeping Different?
SeaKeeping is a unique and powerful analysis tool. Below are a just a few reasons why SK is different from the competition:
SeaKeeping Features
The module offers users the following features: Don't see a specific feature on the list? Contact Customer Support to inquire about current and prospective feature updates. SeaKeeping is always being updated and improved.

SeaKeeping Output
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:

  1. INPUT SUMMARY
  2. Summary of general input parameters, including method type, meshing parameters. coupling parameters, and a table of seakeeping geometry part\component names and types.
  3. CRITICAL POINTS
  4. Table of user specified Critical Points, overall vessel CG, and any optional derived response points (SHW, MSI).
  5. CASE(S)
  6. Case number, case-specific wave heading and ship speed
    1. Wave Components
    2. Summary of overall wave/spectra type, wave samples, sampling method parameters, and numerically derived variance and significant wave height. Also includes tabulated wave period, frequency, LWL/WvLen, encounter frequency, ordinate, and amplitude for each wave component.
    3. RAOs and Phase Angles (Position, Velocity, and/or Acceleration)
    4. 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.
    5. Response Statistics (Position, Velocity, and/or Acceleration)
    6. 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.
    7. Derived Responses (Optional)
      1. Slamming
      2. Deck Submergence/Shipping Water "SHW"
      3. Point Emergence "EMG"
      4. Motion Sickness Incidence "MSI"
    8. Case Summary Table (Optional)
    9. Table of user requested absolute response amplitudes for all modes for each Critical Point. Displays the response for the preceding case.
  7. POLAR PLOTS (Optional)
  8. Polar plots for each user requested response for each Critical Point for all modes.
  9. LIMIT PLOTS (Optional)
  10. Polar limit plots for each user defined dynamic limit over all cases.
  11. OVERALL SUMMARY TABLE (Optional)
  12. Table of overall user requested absolute response amplitudes and corresponding case numbers 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. Automated response and limit polar plotting is also available to further aid in the review process.

In addition to comprehensive reports, SeaKeeping offers seven (7) optional comma-separated-variable (CSV) data files that include any of the information found in the report (and more) in a convenient form for input into spreadsheets, third-party programs, or further post-processing by run files.

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.

Validation Studies
A number of core validation studies, including coefficients, forcing, RAOs, relative motions, and accelerations, may be found here.

SK Q&A
A collection of common questions from SK users may be found here.

Publications Featuring SK

Kyle E. Marlantes, Peter Kim. Addressing the New IMO Guidelines for Second Generation Intact Stability. MarineLink: November, 2020.
Abstract: The common perception of intact stability has remained largely unchanged over the last few decades, where a vesselís stability is evaluated using classical and static means: limits on righting arms, residual areas, and determining maximal VCG (or minimal GM) composite curves. These methods are familiar to most naval architects and are taught at a fundamental level in most naval architecture engineering programs. But repeated incidents of dynamic failure in recent decades brings question to the adequacy of classical static stability criteria to provide a complete understanding of, and adequate safety margin for, a vesselís stability. Obviously, strictly static methods are not wholly sufficient in assessing the dynamic stability of a vessel in waves. Stability criterion are designed to protect people and property, and with safety and liability a primary concern, an improved regulatory framework to assess dynamic stability is required.

Marlantes, K. E. (2019, October 30). Asymmetric Conditions and Ship Motions: Investigating the Ubiquitous Symmetry Assumption. The Society of Naval Architects and Marine Engineers.
Abstract: This paper explores the effect of asymmetric conditions, specifically non-zero heel, on the formulation of the ship motion problem using a fully-coupled, linear seakeeping code developed by the author. A theoretical formulation is provided under the auspices of an eliminated symmetry assumption, and numerical predictions of the radiation and excitation forces are given to explore unique aspects of the problem. Symmetric and asymmetric numerical heave, roll, and pitch RAOs for a generic naval frigate are compared to third-party model test data. It is found that asymmetry can have marked effects on the ship motions problem, most notably in the roll excitation moment, physical mass matrix, and the hydrodynamic cross-coupling of the six modes of motion. The location of a so-called ďcenter of motionĒ is found to be important in the formulation, suggesting that the origin cannot be arbitrarily placed at the center of mass. Some discussion addressing the practical nature of asymmetry in seakeeping computations is provided, attempting to relate the theoretical and numerical findings back to the practical application.

Kyle E. Marlantes, Brandon M. Taravella, A fully-coupled quadratic strip theory/finite element method for predicting global ship structure response in head seas, Ocean Engineering, Volume 187, 2019, 106189, ISSN 0029-8018.
Abstract: This paper outlines the theoretical development and some validation of a quadratic strip theory method coupled to a global finite element model to predict the global structural response of the Korea Research Institute of Ships and Ocean Engineering (KRISO) hull geometry due to regular, head seas waves in the time-domain. The method attempts to capture some body-nonlinear effects of the dynamic problem due to time-varying underwater hull geometry by drawing a relationship between the coefficients, A33, B33, and C33 and the local draft, Ts. In addition, the hull girder is considered flexible and structural damping may be included. A segmented model test in head seas was also performed, and the linear and nonlinear numerical results are compared to the experimental data. It is found that the theory shows reasonably good agreement with the model test data, and that nonlinear effects account for a significant increase in predicted bending moment.

GHS-SK: An Integrated, General-Purpose Approach to Seakeeping and Hydrodynamic Analysis
Abstract: The General HydroStatics SeaKeeping software module, referred to in short as "SK", is Creative Systemsí entrant into the world of hydrodynamics. Introduced in January of 2018, the module aims to provide users with an integrated, general purpose approach to seakeeping and hydrodynamic analysis. This paper is a moderately technical introduction for the interested individual or prospective SK user. After some introduction, the overall focus will be on the four (4) main areas that make SK unique in its class: Automation, Customization, Technical Capability, and Development & User Support. While some theoretical content is presented here, those specifically interested in a deeper mathematical basis of the module are invited to contact Creative Systems Inc. for a copy of the SK Userís Manual.

Kyle E. Marlantes. Tech Talk: GHS Adds 'Seakeeping'. MarineLink: February, 2018.
Abstract: General HydroStatics is no longer just about hydrostatics, and will soon offer capabilities in the world of hydrodynamics with the introduction of a long awaited addition to the GHS product family: an optional seakeeping module.




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