Output Files

HydroDyn produces four types of output files: an echo file, a wave-elevations file, a summary file, and a time-series results file. The following sections detail the purpose and contents of these files. Echo Files

If you set the Echo flag to TRUE in the HydroDyn driver file or the HydroDyn primary input file, the contents of those files will be echoed to a file with the naming conventions, OutRootName.dvr.ech for the driver input file and OutRootName.HD.ech for the HydroDyn primary input file. OutRootName is either specified in the HYDRODYN section of the driver input file, or by the FAST program. The echo files are helpful for debugging your input files. The contents of an echo file will be truncated if HydroDyn encounters an error while parsing an input file. The error usually corresponds to the line after the last successfully echoed line. Wave-Elevations File

Setting WaveElevSeriesFlag in the driver file to TRUE enables the outputting of a grid of wave elevations to a text-based file with the name OutRootName.WaveElev.out. The grid consists of WaveElevNX by WaveElevNY wave elevations (centered at X = 0, Y = 0) with a dX and dY spacing in the global inertial-frame coordinate system. These wave elevations are distinct and output separately from the wave elevations determined by NWaveElev in the HydroDyn primary input file, such that the total number of wave elevation outputs is NWaveElev + ( WaveElevNX × WaveElevNY ). The wave-elevation output file OutRootName.WaveElev.out contains the total wave elevation, which is the sum of the first- and second-order terms (when the second-order wave kinematics are optionally enabled). Summary File

HydroDyn generates a summary file with the naming convention, OutRootName.HD.sum if the HDSum parameter is set to TRUE. This file summarizes key information about your hydrodynamics model, including buoyancy, substructure volumes, marine growth weight, the simulation mesh and its properties, first-order wave frequency components, and the radiation kernel.

When the text refers to an index, it is referring to a given row in a table. The indexing starts at 1 and increases consecutively down the rows. WAMIT-model volume and buoyancy information

This section summarizes the buoyancy of the potential-flow-model platform in its undisplaced configuration. For a hybrid potential-flow/strip-theory model, these buoyancy values must be added to any strip-theory member buoyancy reported in the subsequent sections to obtain the total buoyancy of the platform. Substructure Volume Calculations

This section contains a summary of the total substructure volume, the submerged volume, volume of any marine growth, and fluid-filled (flooded/ballasted) volume for the substructure in its undisplaced configuration. Except for the fluid-filled volume value, the reported volumes are only for members that have the PropPot flag set to FALSE. The flooded/ballasted volume applies to any fluid-filled member, regardless of its PropPot flag. Integrated Buoyancy Loads

This section details the buoyancy loads of the undisplaced substructure when summed about the WRP (0,0,0). The external buoyancy includes the effects of marine growth, and only applies to members whose PropPot flag is set to FALSE. The internal buoyancy is the negative effect on buoyancy due to flooding or ballasting and is independent of the PropPot flag. Integrated Marine Growth Weights

This section details the marine growth weight loads of the undisplaced substructure when summed about the WRP (0,0,0). Simulation Node Table

This table details the undisplaced nodal information and properties for all internal analysis nodes used by the HydroDyn model. The node index is provided in the first column. The second column maps the node to the input joint index (not to be confused with the JointID). If a value of -1 is found in this column, the node is an interior node and results from an input member being split somewhere along its length due to the requirements of the MDivSize parameter in the primary input file members table. The third column indicates if this node is part of a Super Member (JointOvrlp = 1). The next column tells you the corresponding input member index (not to be confused with the MemberID). Nxi, Nyi, and Nzi, provide the (X,Y,Z) coordinates in the global inertial-frame coordinate system. InpMbrDist provides the normalized distance to the node from the start of the input member. R is the outer radius of the member at the node (excluding marine growth), and t is the member wall thickness at the node. dRdZ is the taper of the member at the node, tMG is the marine growth thickness, and MGDens is the marine growth density. PropPot indicates whether the element attached to this node is modeled using potential-flow theory. If FilledFlag is TRUE, then FillDens gives the filled fluid density and FillFSLoc indicates the free-surface height (Z-coordinate). Cd, Ca, Cp, AxCa, AxCp, JAxCd, JAxCa, and JAxCp are the viscous-drag, added-mass, dynamic-pressure, axial added-mass, axial dynamic-pressure, end-effect axial viscous-drag, end-effect axial added-mass, and end-effect axial dynamic-pressure coefficients, respectively. NConn gives the number of elements connected to node, and Connection List is the list of element indexes attached to the node. Simulation Element Table

This section details the undisplaced simulation elements and their associated properties. A suffix of 1 or 2 in a column heading refers to the element’s starting or ending node, respectively. The first column is the element index. node1 and node2 refer to the node index found in the node table of the previous section. Next are the element Length and exterior Volume. This exterior volume calculation includes any effects of marine growth. MGVolume provides the volume contribution due to marine growth. The cross-sectional properties of outer radius (excluding marine growth), marine growth thickness, and wall thickness for each node are given by R1, tMG1, t1, R2, tMG2, and t2, respectively. MGDens1 and MGDens2 are the marine growth density at node 1 and 2. PropPot indicates if the element is modeled using potential-flow theory. If the element is fluid-filled (has flooding or ballasting), FilledFlag is set to T for TRUE. FillDensity and FillFSLoc are the filled fluid density and the free-surface location’s Z-coordinate in the global inertial-frame coordinate system. FillMass is calculated by multiplying the FillDensity value by the element’s interior volume. Finally, the element hydrodynamic coefficients are listed. These are the same coefficients listed in the node table (above). Summary of User-Requested Outputs

The summary file includes information about all requested member and joint output channels. Member Outputs

The first column lists the data channel’s string label, as entered in the OUTPUT CHANNELS section of the HydroDyn input file. Xi, Yi, Zi, provide the output’s undisplaced spatial location in the global inertial-frame coordinate system. The next column, InpMbrIndx, tells you the corresponding input member index (not to be confused with the MemberID). Next are the coordinates of the starting (StartXi, StartYi, StartZi) and ending (EndXi, EndYi, EndZi) nodes of the element containing this output location. Loc is the normalized distance from the starting node of this element. Joint Outputs

The first column lists the data channel’s string label, as entered in the OUTPUT CHANNELS section of the HydroDyn input file. Xi, Yi, Zi, provide the output’s undisplaced spatial location in the global inertial-frame coordinate system. InpJointID specifies the JointID for the output as given in the MEMBER JOINTS table of the HydroDyn input file. The Wave Number and Complex Values of the Wave Elevations as a Function of Frequency

This section provides the frequency-domain description (in terms of a Discrete Fourier Transform or DFT) of the first-order wave elevation at (0,0) on the free surface, but is not written when WaveMod = 0 or 6. The first column, m, identifies the index of each wave frequency component. The finite-depth wave number, frequency, and direction of the wave component are given by k, Omega, and Direction, respectively. The last two columns provide the real (REAL(DFT{WaveElev})) and imaginary (IMAG(DFT{WaveElev})) components of the DFT of the first-order wave elevation. The DFT produces includes both the negative- and positive-frequency components. The negative-frequency components are complex conjugates of the positive frequency components because the time-domain wave elevation is real-valued. The relationships between the negative- and positive-frequency components of the DFT are given by \(k\left( - \omega \right) = - k\left( \omega \right)\) and \(H\left( - \omega \right) = {H\left( \omega \right)}^{*}\), where H is the DFT of the wave elevation and * denotes the complex conjugate. Radiation Memory Effect Convolution Kernel

In the potential-flow solution based on frequency-to-time-domain transforms, HydroDyn computes the radiation kernel used by the convolution method for calculating the radiation memory effect through the cosine transform of the 6x6 frequency-dependent hydrodynamic damping matrix from the radiation problem. The resulting time-domain radiation kernel (radiation impulse-response function)—which is a 6x6 time-dependent matrix—is provided in this section. n and t give the time-step index and time, which are followed by the elements (K11, K12, etc.) of the radiation kernel associated with that time. Because the frequency-dependent hydrodynamic damping matrix is symmetric, so is the radiation kernel; thus, only the diagonal and upper-triangular portion of the matrix are provided. The radiation kernel should decay to zero after a short amount of time, which should aid in selecting an appropriate value of RdtnTMax. Results File

The HydroDyn time-series results are written to a text-based file with the naming convention OutRootName.HD.out when OutSwtch is set to either 1 or 3. If HydroDyn is coupled to FAST and OutSwtch is set to 2 or 3, then FAST will generate a master results file that includes the HydroDyn results. The results are in table format, where each column is a data channel (the first column always being the simulation time), and each row corresponds to a simulation output time step. The data channels are specified in the OUTPUT CHANNELS section of the HydroDyn primary input file. The column format of the HydroDyn-generated file is specified using the OutFmt and OutSFmt parameter of the primary input file.