4.10.3. Output Files

HydroDyn produces three types of output files: an echo file, a summary file, and a time-series file. The following sections detail the purpose and contents of these files.

4.10.3.1. 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 OpenFAST 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.

4.10.3.2. 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, and the radiation kernel for potential-flow bodies.

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.

4.10.3.2.1. WAMIT-Model Volume and Buoyancy Information

This section summarizes the buoyancy of each potential-flow body in its undisplaced position. 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.

4.10.3.2.2. Strip-Theory Volume Calculations

This section contains a summary of the combined total volume, submerged volume, volume of any marine growth, and fluid-filled (flooded/ballasted) volume of all strip-theory members in their undisplaced positions. 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.

4.10.3.2.3. Total Buoyancy Loads

This section details the buoyancy loads of the undisplaced substructure when summed about (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.

4.10.3.2.4. Integrated Marine Growth Weights

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

4.10.3.2.5. Strip-Theory Node Table

This table details the undisplaced strip-theory nodal information and properties for all user defined joints and internal analysis nodes generated by HydroDyn. The internal nodes are generated by splitting input members somewhere along its length to meet the requirements of the MDivSize parameter in the primary input file member table. The node index is provided in the first column. The second column provides the input member index (not to be confused with the MemberID) each internal node belongs to. User-defined joints do not necessarily belong to a specific member, so no information is provided on this column for these joints. Nxi, Nyi, and Nzi provide the (X,Y,Z) coordinates in the global inertial-frame coordinate system. R is the outer radius of the member at the node (excluding marine growth), and t is the member wall thickness 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 FillMass gives the filled fluid mass assigned to the node. Cd, Ca, Cp, Cb, AxCd, AxCa, AxCp, JAxCd, JAxCa, and JAxCp are the transverse drag, transverse added-mass, transverse dynamic-pressure, buoyancy-scaling, axial drag, axial added-mass, axial dynamic-pressure, endplate axial drag, endplate axial added-mass, and endplate axial dynamic-pressure coefficients, respectively. Note that some of the columns are only populated for user-defined joints, while other columns are only populated for internal analysis nodes belonging to a single member.

4.10.3.2.6. Strip-Theory Member Table

This section details the undisplaced strip-theory members and their associated properties. A suffix of 1 or 2 in a column heading refers to the starting or ending node of the member, respectively. The first column is the member index. joint1 and joint2 refer to the node index found in the node table of the previous section. Next are the member Length, the number of subdivided elements NElem to meet the MDivSize requirement, and the exterior Volume. This exterior volume calculation includes any marine growth volume on the member. MGVolume provides the volume contribution due to marine growth. Volume and MGVolume will be zeros for members modeled by potential flow, i.e., with PropPot = T for TRUE. The cross-sectional properties of outer radius (including marine growth) and wall thickness for each node are given by R1, t1, R2, and t2, respectively. PropPot indicates if the member 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 (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 hydrodynamic coefficients at the two end joints are listed. These are the same coefficients listed in the node table (above).

4.10.3.2.7. Summary of User-Requested Outputs

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

4.10.3.2.7.1. Member Outputs

The first column lists the string labels of the data channels, as entered in the OUTPUT CHANNELS section of the HydroDyn input file. Xi, Yi, and Zi provide the coordinates of the output location in the global inertial-frame system when the structure is not displaced. The next column, MemberID, tells you the corresponding input member index. Next are the coordinates of the starting (StartXi, StartYi, StartZi) and ending (EndXi, EndYi, EndZi) nodes of the member containing this output location. Loc is the normalized distance from the starting node of this member.

4.10.3.2.7.2. Joint Outputs

The first column lists the string labels of the data channels, as entered in the OUTPUT CHANNELS section of the HydroDyn input file. Xi, Yi, and Zi provide the coordinates of the output joint in the global inertial-frame system when the structure is not displaced. InpJointID specifies the JointID for the output as given in the MEMBER JOINTS table of the HydroDyn input file.

4.10.3.2.8. 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 frequency-dependent hydrodynamic damping matrix from the radiation problem. The resulting time-domain radiation kernel (radiation impulse-response function), a time-dependent matrix, is provided in this section. n and t give the time-step index and time, which are followed by the entries of the matrix (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. The dimensions of the radiation kernel matrix depend on the number of potential-flow bodies present (NBody) and NBodyMod in the HydroDyn primary input file. If NBodyMod = 1 (full hydrodynamic coupling), the summary file will contain data for a single 6NBody-by-6NBody matrix. If NBodyMod > 1 (no hydrodynamic coupling), the summary file will contain data for NBody 6-by-6 radiation kernal matrices.

4.10.3.3. 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 OpenFAST and OutSwtch is set to 2 or 3, then OpenFAST 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 is always 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.