6.3.3. 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.
6.3.3.1. 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.
6.3.3.2. 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).
6.3.3.3. 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.
6.3.3.3.1. 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.
6.3.3.3.2. 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.
6.3.3.3.3. 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.
6.3.3.3.4. Integrated Marine Growth Weights¶
This section details the marine growth weight loads of the undisplaced substructure when summed about the WRP (0,0,0).
6.3.3.3.5. 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. See Section 7.5.2 for the member splitting rules used by HydroDyn.
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.
6.3.3.3.6. 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).
6.3.3.3.7. Member Outputs¶
The summary file includes information about all requested member output channels.
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.
6.3.3.3.8. Joint Outputs¶
The summary file includes information about all requested joint output channels.
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.
6.3.3.3.9. 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(−𝜔)=−𝑘(𝜔) and 𝐻(−𝜔)=𝐻(𝜔)∗, where H is the DFT of the wave elevation and * denotes the complex conjugate.
6.3.3.3.10. 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
.
6.3.3.4. 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 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.