Description of Program

---

WAMIT is a computer program based on the panel method for analyzing hydrodynamic interactions with floating or submerged bodies, in the presence of ocean waves. WAMIT is available in two versions. The first-order module, Version 6.3, provides all first order quantities and mean drift forces. The second-order module, Version 6.1S, provides complete second-order nonlinear quantities in addition.

The descriptions of these programs are provided below. More detailed technical information is contained in the WAMIT User Manual. Further information and a wide variety of challenging applications are documented in a series of papers.

---

Go To Version 6.1S

Description of Version 6.3

The basic underlying theory is the linear frequency-domain potential representation of the fluid motion. All first-order oscillatory quantities and second-order mean forces are computed in a consistent and efficient manner. Substantial efforts have been devoted to the development and improvement of this program, with many unique features:

Arbitrary three-dimensional body geometry is prescribed, either by conventional low-order panels or by several new options used with the higher-order solution method. The latter include i) the geometric models from the CAD program MultiSurf ii) exact representations of analytic surface and iii) B-spline representations.

Efficient set-up and solution of the linear system of equations are provided by refined subroutines for the Green function and a special iterative solver.

Outputs include the i) added-mass and damping coefficients, ii) Haskind exciting forces/moments, iii) diffraction pressure exciting forces/moments, iv) body motions in waves with optional specification of linearized external force/moment constraints, v) pressures and fluid velocities on the body, vi)pressures and fluid velocities at specified field points, vii) free-surface elevations, viii) drift forces/moments evaluated by momentum conservation and ix) drift forces/moments evaluted by pressure integration. Outputs i) - vii) can be transformed into time domain impulse response functions using a utility program F2T

Options include irregular-frequency removal, analysis of multiple interacting bodies, hydroelastic analysis of flexiable structures using generalized modes and analysis of internal tanks with free surfaces.

Specific new features of the Version 6.3 are as follows:

All six components of the mean drift forces and moments, on a single body or on each body in the multiple body interaction, are evaluated from the momentum flux through the control surface surrounding each body. The computational results are more robust than the pressure integration when the body surface is not smooth, especially for bodies with sharp corners.

A special option can be used to efficiently analyze the wave field generated by one or more wavemakers situated in planes of symmetry.

A symmetry plane can be used when there are flat dipole elements on the plane of symmetry.

A supplementary HST output file is created to output the hydrostatic matrix of restoring coefficients, including generalized modes. When internal tanks are present, the effect of the internal tanks is included in the hydrostatic coefficient output.

Uniform arrays of field points can be input in a more convenient manner.

The DLL library file GEOMXACT has been extended to include several new analytical geometries.

The DLL library file NEWMODES has been extended to include generalized modes to represent a bank of paddle-type wavemakers, and to represent the vertical modes of a vessel with hinges.

Features carried over from Version 6.2 are as follows:

Internal tanks with free surfaces can be analysed either separately or coupled with the dynamics of vessels.

Impulse response functions (IRFs) in the time domain can be evaluated for the output options 1-7 using a utility program F2T. F2T is provided as a separate program along with WAMIT. F2T converts the outputs of WAMIT into IRFs using Fourier transforms.

The separate components of the hydrodynamic pressure and the fluid velocity at the field points due to each of the radiation modes and due to the diffraction field can be output separately. This extension is useful for post-processing when the dynamics of the body are modified.

In the higher-order method, some or all of the body surface can be defined to represent thin structures.

In addition to the added mass and damping, the pressure and the fluid velocity on the body surface and at the field points can be evaluated for zero and infinite wave frequencies

A new output file, wamitlog.txt, is created during the WAMIT run to provide an archival record of the run, including copies of the principal input files, and various auxiliary information.

Features carried over from Version 6.1 are as follows:

The geometry models developed with the CAD program MultiSurf can be used directly in WAMIT in the higher-order method of solution, facilitating effortless transition from geometric design of the structure to the hydrodynamic analysis. This optional new feature requires the additional license of RG2WAMIT, RGKernal and MultiSurf .

The hydrodynamic pressure on the body surface can be evaluated at user-specified points (x,y,z) which are listed in a special input file. This extension, which is available in both the low-order and higher-order solutions, facilitates the integration of WAMIT with structural-analysis codes where the hydrodynamic pressure is required at specified locations.

The separate components of the hydrodynamic pressure on the body surface due to each of the radiation modes and due to the diffraction field can be output separately. This extension is useful for post-processing when the dynamics of the body are modified.

Features carried over from Version 6.0 are as follows:

A powerful higher-order method based on B-splines is added, to complement the conventional low-order panel method used in all previous versions of WAMIT.

In the low-order method, some or all of the body panels can be defined to represent thin plates or appendages of small thickness, such as damper plates or strakes.

Alternative methods are introduced to define the geometry including conventional flat rectangular panels, B-spline representation, and exact definition of the body shape in appropriate subroutines.

Several different generic types of structures are represented explicitly and exactly in a DLL library. These generic structures can be analyzed simply by inputting the relevant dimensions, without the effort required to prepare a conventional panel input file.

Users can extend the DLL library to include other types of structures.

For generalized modes the mode shapes can be defined in a separate DLL file.

New configuration parameters have been added to provide a more unified and flexible range of input formats.

New output files have been introduced to facilitate 3-dimensional plotting of the geometry, conversion from the higher-order geometry to low-order panels, and sub-division or reflection of the low-order panels.

Program execution has been simplified, and run times reduced.

Other extensions which carry over from Version 5.4 include:

Irregular-frequency effects can be removed in both the potential and source formulations.

First-order forces can be computed for a structure with horizontal panels lying in the plane of the free surface.

Field point quantities (pressure and velocity) can be computed from either the potential or source formulation.

Modes analyzed by POTEN may be specified as either free or fixed in FORCE. In place of the conventional RAO's, outputs for fixed modes give the corresponding wave loads without additional post-processing.

There are no maximum limits for the length of any input arrays.

A demonstration version with predefined geometry inputs may be downloaded from this site.  The WAMIT User Manual may also be downloaded.