WINPOST USER’S MANUAL
This User’s manual has been prepared for the JIP sponsors. The program WINPOST is written with
standard FROTRAN 77 language and is expected to be machine independent.
1. INTRODUCTION
WINPOST is a finite element program for the coupled dynamic analysis of moored multi-column
compliant offshore structures, such as TLPs and SPARs. The program performs coupled dynamic
analyses for the platform-mooring (riser) system both in time domain and frequency domain. In the
time domain analysis, various nonlinearities, such as the drag force on the mooring lines and
columns of the platform, the large (translational) motion of the platform, the free surface effects,
and the geometric nonlinearity of the mooring system, are included in the time marching scheme.
In the frequency domain analysis, the platform--mooring system is assumed undergoing small
motions around the mean position so that a linear analysis can be applied. Meanwhile, the drag
forces on the mooring lines and columns of the platform are linearized using a statistical
linearization technique (Rodenbush et al, 1986). Except the drag force, all the hydrodynamic forces
on the platform, which include first-order and second-order sum- and difference-frequency potential
forces, are computed from a hydrodynamics program WINTCOL and the computed results are
imported into WINPOST for the ensuing analysis. Therefore, WINPOST serves as a “postprocessor” of the program WINTCOL.
In WINPOST, the environmental inputs include regular and irregular waves, current, and steady
wind force on the platform. The program does not compute dynamic wind forces. Nevertheless, it
can read, if necessary, the dynamic-wind-force time series from a user pre-generated data file and
include it in the time marching scheme.
In WINPOST, the elastic rod model is used for modeling the mooring system. This model is ideal
for small strain, large displacement structural analysis of slender members such as tether, riser and
catenary mooring lines. A single global coordinate system is used in the finite element formulation
of the rod model. Therefore, the model is simpler and more efficient than other conventional
nonlinear models, such as the updated Lagrangian beam model. Detailed theory and finite element
modeling of the rod can be found in Nordgren (1974) and Garrette (1982). In WINPOST, the
model was improved to include the stretch of the element under the axial tension. Special situations
such as water surface piercing and sea bottom lying of the mooring lines (risers) are also considered
in the program.
In WINPOST, the platform is assumed to be a rigid body undergoing small (rotational) motions in
waves, wind and current. Under this assumption, time domain hydrodynamic forces on the
platform, including second-order sum- and difference-frequency forces, can be generated using the
information from frequency-domain computations (Ran & Kim, 1995,1996). The viscous effect on
the platform is also included in the form of Morison’s drag formula if the platform is formed by
relatively slender elements.
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In WINPOST, the connections between the platform and mooring are modeled by linear
translational/rotational springs, and linear translational dampers. By controlling the stiffness
coefficients of these springs, various types of connections including hinged and fixed connections
can be modeled. The connections between the foundations and the moorings can be similarly
modeled in addition to using conventional boundary conditions.
The program WINPOST can also perform uncoupled motion analyses for the platform with user
defined restoring-stiffness modeling of the mooring system. It can also perform uncoupled motion
analyses for the mooring (riser) system provided that the motion of the platform is given by users.
The program also has an option that allows users to define the wave components for random waves.
This option is useful if the time history of an incident wave is known. Otherwise, the phases of
component waves are generated from a random-number generator. For example, the user can use
FFT to obtain the wave components (amplitudes and phases) from the wave elevation time history
of a model test and input them into WINPOST so that a direct comparison of motion (or force)
time series, instead of statistics, can be made between the simulation and the model test for the same
wave.
Since the WINPOST is an independent program which reads the hydrodynamic information of the
platform from a data file, it can also be used with other hydrodynamic programs such as WAMIT.
In that case, users need to make sure that the hydrodynamic information follows the format of
WINPOST when preparing the input data files.
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2. PROGRAM COMPILING AND RUNNING
The program consists of two files: WINPOST.FOR and WPARA.BLK. The first file contains all
the source codes of the program, and the second file specifies the parameters that control the
dimensions of the variables used in the program. These parameters are explained in the file
WPARA.BLK and users can easily make changes if necessary. It is recommended that users always
check the file WPARA.BLK when they prepare new input data files to ensure that the dimensions
of the variables are large enough for the type of analysis they want to do. Users need to re-compile
the program WINPOST.FOR whenever a change is made in the file WPARA.BLK.
The program has been tested under UNIX and VAX operating systems on a work station, and
WINDOWS NT on a PC (with Watcom FORTRAN compiler). Depending on the variable size,
which is defined by the parameter in WPARA.BLK, the memory size required by the program varies
significantly. It is recommended to have over 64 MB of memory size on PC to run the program
efficiently.
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3. INPUT DATA FILE
There are at least two input data files to be prepared by users. The first one, WINPOST.IN,
contains the information about mooring system (element definition, material property, platformmooring coupling, mooring line boundary conditions) and run-time command. The second file,
WINPOST.WV, contains hydrodynamic data from WINTCOL (added mass, radiation damping,
first-order forces and second-order sum- and difference-frequency forces, and wave drift damping),
wave and current parameters, and information about platforms.
The input and output data are dimensional and standard unit systems are used (meters, kg, Newton
and second for SI system; feet, slug, lb and second for English system). The name of each input data
in the input file follows the convention of FORTRAN Language, i.e., the variables starting from I to
N are integers, otherwise, the data are real numbers. The data given in {} are needed only for threedimensional analyses.
There are two coordinate systems in the program: global coordinate system and rigid-body
(platform) coordinate system. In the 3D analysis, the x and y axis define a horizontal plane and z
axis is positive upward. In the 2D analysis, x-z coordinate system is used with z axis positive upward.
The origins of both the global and rigid-body coordinate systems are located on the mean water
surface with the corresponding axis parallel to each other. All the information related to the mooring
system is defined with respect to the global coordinate system. On the other hand, hydrodynamic
quantities for the platform are given with respect to the rigid-body system. In the following
sections, all the input and output data are given in global coordinate except those specified
otherwise.
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3.1 WINPOST.IN
The input data in WINPOST.IN can be divided into four groups. The first group of data contains
general information needed in the program and is listed as follows
NDIM, NLEG, NMAT, GRAVITY, RHOW
MITER, NSTEP, DT, NINT
BTTM, CB
BX0(1), BX0(2), {BX0(3)}
In this group, NDIM defines the dimension of the analysis. It is 2 for two-dimensional analysis and
3 for three-dimensional analysis. NLEG is the total number of tethers, risers and mooring lines in
the analysis. In the following, the tethers, risers, and mooring lines are referred as “legs”. NMAT is
the total number of sets of material properties in a mooring system. GRAVITY is the gravitational
acceleration. GRAVITY=9.8065 in SI unit system, and GRAVITY=32.17 in English unit system.
RHOW is the water density. MITER is the maximum number of iterations specified in the static
analysis. In the static analysis, the nonlinear equation is solved by using Newton iteration scheme. If
the tolerance that is specified later in the file is not satisfied after MITER iterations, the program will
stop and print a massage on screen. NSTEP is the total number of steps and DT is the time interval
in the time-marching scheme. The accuracy of the time domain simulation is primarily controlled by
the time interval, namely, the value of DT. In general, a stronger nonlinear problem requires smaller
time interval. For instance, in the coupled analysis of TLP or SPAR, it is recommended that the DT
have a value that allows at least 30 time steps in the smallest period of interest. The NINT is a
parameter that controls the output in the time domain simulation. The program will output the
results for every NINT steps in the time domain simulation. This allows the user to control the
amount of output data without changing the time interval DT. For example, with time interval
DT=0.005 seconds, the program will output the results for every 0.005 second interval if NINT=1,
and will output the results for every 0.1 second interval if NINT=20. BTTM is the vertical
coordinate (should be negative) of a horizontal foundation (sea floor) and CB is the stiffness
coefficient of the foundation. Those two variables are used for the mooring lines or flexible risers
with part of the line lying on the sea floor. In the program, the elastic foundation is modeled as a
continuous quadratic spring foundation to support the lines, The relation between the vertical
support force F and the vertical deformation dz is F=CBdz2. Keep in mind that usually the BTTM
has the same value as water depth, but it is not used to calculate wave kinematics. The water depth
for wave kinematics is defined in the other input file WINPOST.WV. BX0 defines the position (in
global coordinate system) of the origin of the local rigid-body coordinate system.
Every parameter in the above group must be given by the user even if it is not used in the analysis.
For example, even if there is no foundation lying element in the analysis, arbitrary numbers should
be given to the parameter BTTM and CB.
The second group of data in WINPOST.IN contains all the material properties of the legs. In
WINPOST, each leg is described by a finite number of rod elements. The material properties
(stretch and bending stiffness, etc.) are constant in each element. However, they may vary from
element to element so that a non-uniform leg such as a mixed wire-chain mooring line can be
modeled. There will be NMAT sets of material properties with NMAT being the total number of
sets as given in the first group. The input format for material properties is as follows:
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GAE1, GEI1, GRHOL1, GRHOA1, GCI1, GCD1, GAS1
...
GAEn, GEIn, GRHOLn, GRHOAn, GCIn, GCDn, GASn
...
GAENMAT,GEINMAT,GRHOLNMAT,GRHOANMAT,GCINMAT,GCDNMAT,GASNMAT
where GAE is the axial stiffness (Young’s modulus  cross sectional area of the leg), and GEI is the
bending stiffness (Young’s modulus  moment of inertia of cross section). GRHOL is the mass per
unit length of the element, and GRHOA is the displaced mass per unit length if the element is in
water (GRHOA=0 if the element is in air). GCI is the coefficient of inertial force, i.e., the inertia
force per unit length at unit acceleration. GCD is the coefficient of drag force, i.e., the drag force
per unit length at unit relative velocity. GAS is the cross sectional area of the element. GAS is only
used in calculating axial stretch of the element in water. If the actual cross section is used, the
stretch is computed using actual tension in the element. If GAS=0, then the stretch is computed
using effective tension (effective tension = actual tension + hydrostatic pressure  GAS).
The third group of input data in WINPOST.IN contains information about legs. This group of data
must be prepared for every leg. In other words, one should repeat this group of input data for
NLEG times, where NLEG is the total number of legs as defined in group one. The first two
parameters in this group are
NELEM,IFLAG1
NELEM is the total number of elements in a leg, and IFLAG1 is a flag defining two ways of
inputing the elements’ geometry . If IFLAG=0, the elements are defined in the following format:
R(1)1,R(2)1,{R(3)1},RP(1)1,RP(2)1,{RP(3)1},TZER1
...
R(1)n,R(2)n,{R(3)n},RP(1)n, RP(2)n, {RP(3)n}, TZERn
...
R(1)NELEM+1,R(2)NELEM+1,{R(3)NELEM+1},
RP(1)NELEM+1,RP(2)NELEM+1,{RP(3)NELEM+1}, TZERNELEM+1
GLEN1, IOPTN1, MAT1
...
GLENn, IOPTNn, MATn
...
GLENNELEM, IOPTNNELEM, MATNELEM
where Rn is the nodal coordinate of the n-th node in the leg, and RPn is the unit tangential vector
(directional cosine) of the leg at that node. The tangential vector of a node always points to the
direction of a higher numbered node nearby. There are a total of NELEM+1 nodes in the leg. The
nodal numbering should be in a consecutive manner from one end to the other end of the leg. For
a coupled analysis, the first node in a leg should be at the end which is connected to the bottom
boundary (sea floor), and the last node should be at the other end of the leg which is connected to
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the rigid body (platform). For an uncoupled analysis, the numbering of the nodes can start from
either ends of the leg. TZERn is the pretension in the leg at n-th node. This input affects axial
deformation of the element in the analysis. For example, in a TLP analysis, if the stretch of the
tether caused by the net buoyancy force is already included in the initial element length (GLEN),
one needs to set the TZER as the actual static pretension so that any axial deformation in the
calculation is caused only by dynamic tension. GLENn is the length of the n-th element that is
between node n and n+1. IOTPN is an option for each element. It is 1 if that element touches or
is likely to touch the foundation (sea floor), and 2 if that element is at or near free surface and likely
to pierce the water surface. Otherwise, it is 0. When IOTPN=1, the program will check whether
that element touches the foundation and whether the stiffness matrix of the element needs to be
modified to include the contribution of the foundation. When IOPTN=2, the program will check
the position of free surface with respect to the element and change the added mass and
hydrodynamic force computation accordingly. MATn is the set number of the material properties
for the n-th element. All sets of the material properties are previously defined in the second group.
The above input format for the element geometry is suitable for the legs whose initial positions are
known, such as the vertical tether of a TLP. However, it is inconvenient to use this format for a
catenary mooring line since the initial nodal positions of the lines are not easy to find. In that case,
user can use a more convenient format by setting IFLAG=1.
If IFLAG1=1, the following format for the definition of element position should be used:
PA(1), PA(2), {PA(3)}
PB(1), PB(2), {PB(3)}
GLEN1, IOPTN1, MAT1,TZER1
...
GLENn, IOPTNn, MATn, TZERn
...
GLENNELEM, IOPTNNELEM, MATNELEM, TZERNELEM+1
where the PA is the nodal position of the first node, and PB is the nodal position of the last node.
For coupled analysis, the first node in a leg should be at one end which is connected to the bottom
boundary (sea floor), and the last node should be at the other end of leg which is connected to the
rigid body (platform). The definitions for GLEN, IOPTN, MAT and TZER are the same as those
for IFLAG=0.
Following the element geometry input, leg boundary conditions and other information for each leg
are to be given as follows:
NBVP
IBVP(1)1,IBVP(2)1,IBVP(3)1,BVP1
...
IBVP(1)NBVP,IBVP(2)NBVP,IBVP(3)NBVP,BVPNBVP
NBVS
IBVS(1)1,IBVS(2)1,IBVS(3)1,BVS1
...
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IBVS(1)NBVS,IBVS(2)NBVS,IBVS(3)NBVS,BVSNBVS
NEND1
GSL(1),GSL(2),{GSL(3)},GSR,GE(1),GE(2),{GE(3),}
GX(1),GX(2),{GX(3)}
GDL
NEND2
GSL(1),GSL(2),{GSL(3)},GSR,GE(1),GE(2),{GE(3),}
GX(1),GX(2),{GX(3)}
GDL
NOUT
NEOUT(1), ..., NEOUT(NOUT)
where NBVP is the total number of essential (displacement) boundary conditions in the leg. If it is
not 0, for each essential boundary condition, users need to define: IBVP(1)--the nodal number
where boundary condition applies; IBVP(2)--the direction of the boundary condition (1 in x, 2 in z
direction for 2D analysis; 1 in x, 2 in y and 3 in z direction in 3D analysis); IBVP(3)--is 1 if the
boundary condition is to define the position of the node and 2 if the boundary condition is to
define the unit tangential vector of the node; BVP-- the value of the boundary condition. For
example, an input of 8,1,1,20.0 means that the x coordinate of node 8 is 20.0 (in global coordinate
system). As an another example, the input of 23,3,2 0.7 means that the z component of the unit
tangential vector at node 23 is 0.7.
Similarly, NBVS is the total number of natural (force) boundary conditions. If it is not 0, for each
natural boundary condition, users need to define: IBVS(1)--the nodal number where boundary
condition applies; IBVS(2)--the direction of the boundary condition (1 in x, 2 in z direction for 2D
analysis; 1 in x, 2 in y and 3 in z direction in 3D analysis); IBVS(3)--is always 1; BVS--the value of
the external force applied. For example, an input of 11,2,1,2.0e5 means that 2.0e5 (Newton or lb.)
of force is applied in the y direction on node 11.
For the nodes at the two ends of the leg, special boundary conditions are considered in addition to
the ones described above. The ends can be connected to the boundary or rigid body (platform) by
linear translational and rotational springs, and linear translational dampers. NEND1 is a flag for the
first end (node 1). It is 1 if the end is connected to the boundary by springs and damper, and 0 if
not. If NEND1=1, one needs to input the following information of spring and damper connection:
GSL--the linear spring stiffness (unit: force/length) in each direction; GSR--the rotational spring
stiffness (unit: moment/radian); GE--the unit vector defining the rotational spring reference axis.
A moment will be created if there is a non-zero angle between the unit tangential vector at the end
of the leg and the reference axis GE. GX is the position of the point on the boundary where the
linear springs are connected; GDL is the damping coefficient (unit: force/velocity) of the damper.
A damping will be created if there are relative translational velocities between the end of the leg and
connection point on the boundary.
NEND2 is a flag for the other end of the leg (node
NELEM+1) which is connected to a rigid body (platform) or fixed boundary. It is 1 if the end is
connected to a fixed boundary by springs and dampers (this condition is for uncoupled analysis
only), 2 if the end is connected to a rigid body (platform), and 0 if there is no spring and damper
connections at this end (this condition is for uncoupled analysis only). For option 1 or 2, the user
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should input the information about the spring and damper which are defined in a similar manner to
those of the other end. GX will be the position of the connecting point on platform, and GE will
be the unit vector fixed on the rigid body (platform) defining the rotational spring reference axis.
When NEND1=0 or NEND2=0, springs and dampers are not used for the boundary condition.
For instance, hinged and fixed joints can be easily modeled by using only essential boundary
conditions without springs and dampers. However, for a coupled analysis, the spring and damper
connections must be used between platform and legs. The user can vary the stiffness to simulate
different types of connections. For instance, a large translational spring stiffness and zero rotational
stiffness can simulate a hinged connection between platform and legs; Sufficiently large values for
both translational and rotational stiffness can simulate a fixed connection. In these cases, it is
recommended that the values of GSL and GSR should be about 1,000~10,000 times higher than
the axial (stretch) stiffness (GAE) and bending stiffness (GEI) of the legs, respectively.
NOUT is the total number of elements that users want to output the nodal reaction forces of the
elements, and NEOUT is the element number.
The last data group in WINPOST.IN contains run-time commands. It defines what kind of analysis
program will perform. The parameters in this group are listed as follows,
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
...
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
...
0
where NSIGNAL tells the program to continue (=1) or to stop (=0) calculation. If NSIGNAL is 1,
users need to define: IPT1--is 0 for static analysis, 1 for time-domain dynamic analysis, and -1 for
frequency-domain analysis; IPTP2--is 1 if hydrodynamic forces on the leg and platform are
considered, 0 if no hydrodynamic force included, and 2 for a static analysis with linearized drag
forces (this option is used to find a new mean position after a frequency-domain analysis is
performed); IPT3-- is 0 if axial stretching of the leg is considered and 1 if the leg is assumed
inextensible; IPT4-- is 1 for the coupled analysis, 0 for the uncoupled leg analysis only, and 2 for
time-domain analysis for the rigid body (platform) only. TEMP is the tolerance for the static
analysis (when IPT1=0) or frequency-domain analysis (when IPT1=-1), and is the number of steps
for ramp in time-domain analysis (when IPT1=1). In the time-domain analysis, the external forces
on the platform and legs are gradually increased from zero to full value in the first TEMP steps to
minimize the numerically induced transient motion.
The following shows some examples of the command lines for different types of analyses:
a)
1
0 0 0 0 1e-6
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
9
With this command, the program will perform static analysis (IPT1=0) for the axially extensible
(IPT3=0) legs only (IPT4=0) without environmental forces (IPT2=0). The tolerance of the
static analysis is 1e-6. There may be more than one leg in the analysis. If the input is for a
coupled platform/mooring system and one end of the leg is connected to the platform, this
analysis will be performed with a platform fixed at the initial position as defined in the input file.
For a coupled platform/mooring system, in order to avoid slow-convergence problem, users can
use this command line to find the equilibrium of the legs (especially the catenary lines) only, then
use the following command to find the equilibrium for the coupled system.
b)
1
0 0 0 1 1e-6
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
With this option, the program will perform static analysis for the coupled system. Environmental
forces are not considered in the analysis. The tolerance of the static analysis is 1e-6.
c)
1
0 1 0 1 1e-6
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
With this option, the program will perform static analysis for the coupled system (IPT4=1) with
environmental forces (IPT2=1). The tolerance of the static analysis is 1e-6. The environmental
forces include steady current forces and mean drift forces. This command line is useful to
quickly find the mean position of the system in waves and currents using the static analysis.
d)
1
1 1 0 1 5000
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
With this option, the program will perform time-domain dynamic analysis (IPT1=1) for the
coupled system (IPT4=1) with the wave and current forces (IPT2=1) increased gradually from
zero to full values in the first 5000 time steps.
e)
1
1 1 0 0 5000
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
With this option, the program will perform time-domain analysis for the uncoupled legs only
(IPT4=0) with the wave and current forces increased gradually from zero to full values in the
first 5000 time steps. If the option NEND2=2 (the second end of the leg is connected to the
platform), the program will read platform motions at each time step from the input file
“WBODY.IN” in the simulation. In this case, users need to make sure that the time interval of
platform motions is the same as that used in the simulation. The format of “WBODY.IN” will
be described later in this manual.
f)
1
1 1 0 2 5000
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
10
With this option, the program will perform time-domain analysis for the uncoupled platform
only (IPT4=2) with the wave and current forces increased gradually from zero to full values in
the first 5000 time steps. The information of the legs will be ignored even if they are read from
the input file. To perform the uncoupled analysis, users need to modify the restoring stiffness
matrix BSTIFF, which is defined in the input file WINPOST.WV, to additionally include the
contributions of the mooring system as massless linear springs. If this equivalent mooring
contribution is not added, we can simulate platform motions without mooring.
g)
1
-1 1 0 1 1e-3
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
With this option, the program will perform frequency-domain analysis (IPT1=-1) for the
coupled system (IPT4=1) with environmental forces, with a tolerance of 1e-3.
h)
1
0 2 0 1 1e-6
NSIGNAL
IPT1,IPT2,IPT3,IPT4,TEMP
With this option, the program will perform static analysis for the coupled system using linearized
drag force (IPT2=2) on the legs and platform after a frequency-domain analysis is performed.
This command line is used to find the updated (more accurate) mean position of the system
which can be used for another round of frequency-domain analysis. The tolerance of the static
analysis is 1e-6.
Before doing any time-domain or frequency-domain analyses, users always need to do a static
analysis either to avoid transient motions caused by the imbalance of a system in the time-domain
analysis, or to find the mean position for the frequency-domain analysis.
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3.2 WINPOST.WV
The input file WINPOST.WV consists of two groups of data. The first group is for the
hydrodynamic information of a platform and is automatically generated in the file WINPOST.WV
when users run the program WINTCOL. The data created by WINTCOL include: the total number
of wave frequencies (NFRE), wave frequencies (FREQT), total number of wave headings (NHD),
wave headings (HEADT), added mass (RINER), radiation (wave) damping (DAMP), first-order
wave forces (WF1), wave drift damping (WDD), second-order difference- (WF2D) and sumfrequency (WF2S) forces, hydrostatic stiffness matrix (BSTIFF), mass matrix (BMASS), net
buoyancy force on the platform (BUOY), total number of columns (NCLMN), horizontal
coordinate of the center and draft (XCLMN), and radius (RCLMN) of each column. All the data
above are given with respect to the rigid-body coordinate system. If WINTCOL is not used, users
need to prepare this group of input data using other hydrodynamics programs, such as WAMIT. For
this, one needs to refer to the subroutine WAVESETUP for the format of the above hydrodynamic
input data. (For more details, see Appendix)
The second group is for environmental conditions. Its format is as follows:
HS,TP,GAMA,BETAWV,FREMIN,FREMAX,VC,BETAC,DEPTH
NFRESP,NHDSP,NSPREAD,IRAND
NFRE2D
FRE2D(1), ... , FRE2D(NFRE2D)
NFRE2S
FRE2S(1), ... , FRE2S(NFRE2S)
NCPRFL
CRPT(1)1,CRPT(2)1
...
CRPT(1)n,CRPT(2)n
...
CRPT(1)NCPRFL,CRPT(2)NCPRFL
IFILE
IPTW1
NTRUS
X11,Y11,Z11,X21,Y21,Z21,CM1,CI1,CD1,FLAG1
...
X1NTRUS,Y1NTRUS,Z1NTRUS,X2NTRUS,Y2NTRUS,Z2NTRUS,CMNTRUS,CINTRUS,CDNTRUS,FLAG NTRUS
NPLAT
X1,Y1,Z1,EX1,EY1,EZ1,CM1,CI1,CD1
…
XNPLAT,Y NPLAT,Z NPLAT,EX NPLAT,EY NPLAT ,EZ NPLAT,CM NPLAT,CI NPLAT,CD NPLAT
12
Waves and currents are defined in the first two lines. HS is the significant wave height; TP is peak
period; GAMA is the overshooting parameter. If GAMA=0, the two-parameter PM spectrum is
used to generate random waves in the program. Otherwise, the random wave is defined by the
JONSWAP spectrum. Users can also define other sea spectra and this option will be explained later.
BETAWV is the main direction of waves in degrees; FREMIN and FREMAX are minimum and
maximum cut-off frequencies of the input spectrum; VC is the current velocity at water surface;
BETAC is the current direction in degrees; DEPTH is the water depth; NFRESP is the number
of wave frequency components that will be generated in the program; NHDSP is the number of
wave headings that will be generated in the program; NSPREAD is the directional spreading
parameter i.e. factor n of cosine to the 2n-th power. For unidirectional waves (NHDSP=1), the
parameter is ignored in the program. IRAND is the random seed (a large negative integer) used in
the program to generate random numbers. If a regular wave is desired, users need to set NFRESP
and NHDSP to be 1, and the wave height and wave period are determined by HS and TP, while all
the other parameters for random waves are ignored. In the frequency domain analysis, the IRAND should
be 1.
NFRE2D is the total number of low frequencies users want to input, and the FRE2D is the
corresponding low-frequency components. Similarly, NFRE2S is the total number of high
frequencies and the FRE2S is the corresponding high-frequency components. These low and high
frequency components are to be used in the frequency domain analysis only. Thus the NFRE2D and NFRE2S
should be set to zero in the time domain analysis. Users should be careful in choosing these low and
high frequencies so that they are near the natural frequencies of a structure (for example, low
frequencies should be near surge and sway natural frequencies, and high frequencies near the pitch
and heave natural frequencies of a TLP) and have enough frequency components to accurately
predict the low- and high-frequency resonant motions.
The parameter NCPRFL is used to define the profile of current velocity. If NCPRFL=0, the
current velocity profile is assumed to follow the 1/7 power rule (current velocity = VC 
(1+z/DEPTH)1/7 , where z is the vertical position). The user can also define an arbitrary current
profile by using the user-defined piece-wise linear current velocity profile. In this case, NCPRFL is
to be greater than 1, and NCPRFL represents the total number of points used to define the current
profile along the depth. In such a case, users need to define CRPT(1)n, the vertical position of the
n-th point (always negative), and CRPT(2)n, the corresponding current velocity at the n-th point.
The order of these points should be from the water surface toward the sea floor.
The user can include a constant wind force on a platform by adding appropriate forces (in rigid
body coordinate system) and moments to the force vector BOUY in WINPOST.WV. The BOUY
is originally generated by WINTCOL and contains only net buoyancy forces. The program does not
generate dynamic wind forces with IFILE=0. The program can include dynamic wind forces in the
time domain simulation by reading them from a file named “WINDF.IN”. In that case, users need
to set IFILE=1 and prepare the dynamic wind force data file. The format of the file is described
later in the manual.
The wave components are generated from a PM or JONSWAP spectrum inside the program and a
random phase is given to each wave component. If users want to use other input spectra, or to
conduct dynamic analyses for a pre-described wave elevation time history (to compare with model
test results, for example), the wave components and their phases can be generated from other input
13
spectra or by using FFT for the wave elevation time history. Those component amplitudes and
phases can be directly input to the program by users. In this case, users need to set IFILE=2 and
prepare a wave-component input file “WCOMP.IN”. The format of the file is described later in the
manual.
If IFILE=3, both the dynamic wind force from the file “WINDF.IN” and the user-defined wave
components in the file “WCOMP.IN” will be used in the time-domain analysis. If IFILE=0, there
exist no dynamic wind force and user-defined wave components, thus users need not prepare those
two files.
The next parameter define what kind of hydrodynamic forces will be included in the calculation:
IPTW1 is 1 for total wave forces; 2 for linear wave force only; 3 for difference-frequency force only;
4 for sum-frequency force only; 5 for the total wave force excluding pontoons (e.g. SPAR).
The next group of parameters define the truss element in the rigid body. NTRUS is the total
number of truss element. If NTRUS is not zero, user needs to define: X1,Y1,Z1--the position of the
first end of the truss (in local coordinate system); X2,Y2,Z2--the position of the second end of the
truss; CM,CI,CD--the added mass, inertia and drag coefficients i.e. CM is the added mass of truss
per unit length, CI is the inertia force per unit length at unit acceleration and CD is the drag force
per unit length at unit relative velocity; FLAG—is 1 if the element is at or near free surface and
likely to pierce the water surface, and is 0 otherwise.
The last group of parameters define the plate element in the rigid body. NPLAT is the total number
of plate element. If NPLAT is not zero, user needs to define: X,Y,Z--the position of the force
center of plate (in local coordinate system); EX,EY,EZ--the three components of the unit normal
vector of the plate (the vector is perpendicular to the plate); CM,CI,CD--the added mass, inertia
and drag coefficients i.e. CM is the added mass of plate, CI is the inertia force on the plate at unit
acceleration and CD is the drag force on the plate at unit relative velocity.
For an uncoupled tether, catenary mooring line and riser analysis, the hydrodynamic information of
the platform is not needed. Thus users only need to prepare the second group of input data
(starting from wave definition ). If the hydrodynamic force is not needed in the uncoupled analysis
(IPT2=0), the file WINPOST.WV is not needed at all.
14
3.3. OTHER OPTIONAL INPUT FILES
Depending on the input parameters in WINPOST.IN and WINPOST.WV, there are three other
input files users may need to prepare. The first one is WBODY.IN. This file is only needed when an
uncoupled dynamic analysis for legs is performed with the second end of the leg connected to (and moving
with) the platform (IPT1=1 and NEND=2). This file contains the 6 degree-of-freedom motions (in
global coordinate system) of the platform at each time step of the time integration. The time
interval of the motion in the file should be the same as the time interval (DT) of the time-domain
simulation. The file has a format as follows:
BX(1)1,BX(2)1,BX(3)1,BX(4)1,BX(5)1,BX(6)1
BX(1)2,BX(2)2,BX(3)2,BX(4)2,BX(5)2,BX(6)2
3
3
3
3
3
3
BX(1) ,BX(2) ,BX(3) ,BX(4) ,BX(5) ,BX(6)
...
where BX(1)--BX(3) are translational motions, and BX(4)--BX(6) are rotational motions of a
platform in x, y and z directions, respectively. The superscript denotes the number of time steps
with step 1 at time t=0. The total number of time steps, or the total number of lines, in the file
should be equal or larger than NSTEP defined in the file WINPOST.IN.
The second file, WCOMP.IN, contains user-defined wave components and their phases. If
IFILE=2 or IFILE=3, the program is to read the wave components and phases from this file
instead of generating them inside the program (using a random-number generator). The file
WCOMP.IN has the following format:
NFRESP
FREQ(1), WAMP(1), PHASE(1)
...
FREQ(NFRESP), WAMP(NFRESP), PHASE(NFRESP)
where NFESP is the total number of wave components; FREQ is the frequency (rad/sec) of each
component; WAMP is the amplitude of each component; PHASE is the phase of each
component in radian. The wave components put in by users are uni-directional with the heading
defined by BATAWV in file WONPOST.WV.
The third optional file is WINDF.IN which contains dynamic wind force time series. When
IFILE=1 or IFILE=3, the program will read the 6 degree-of-freedom dynamic wind forces from
this file in the time-domain simulation. The time interval of the wind force should be the same as
the time interval (DT) used in the time-domain simulation. The file has the following format:
FW(1)1,FW(2)1,FW(3)1,FW(4)1,FW(5)1,FW(6)1
FW(1)2,FW(2)2,FW(3)2,FW(4)2,FW(5)2,FW(6)2
FW(1)3,FW(2)3,FW(3)3,FW(4)3,FW(5)3,FW(6)3
...
where FW(1)--FW(3) are wind-induced forces, and FW(4)--FW(6) are wind-induced moments on a
platform in x, y and z directions, respectively. The forces and moments are to be given with respect
15
to the rigid-body (platform) coordinate system. The superscript denotes the number of time steps.
The total number of time steps, or the total number of lines, in the file should be equal or larger
than NSTEP defined in the file WINPOST.IN.
16
4. OUTPUT FILE
With each run of the program, a set of output data files are created. In the static and time-domain
simulations, the results of every iteration and time step are written in various output files. In the
frequency-domain analysis, only the results of the last iteration are recorded due to the large amount
of data.
The following is the list of output files:
WINPOST.OUT: This file prints out all the input data for rechecking and also contains the
statistics of the time-domain and frequency-domain analyses.
WWAVE.ELE:
This file records wave-elevation time series in the time-domain simulation.
The location where wave elevation is computed is at the origin of the
platform coordinate system (BX0). This point does not move during the
simulation.
WWBODY.DIS This file contains the position of the platform at each iteration of static
analysis, or the platform motions at each output time (in every NINT time
steps) in the time-domain simulation, or the amplitude (complex number) of
the platform motion in the frequency-domain analysis. In the static or timedomain analyses, each line of the file contains the number of iteration or
time step, and 6 degree-of-freedom (or 3 degree-of-freedom in 2D) motions
of the platform. In the frequency-domain analysis, each line of the file
contains the number of the wave components, and the 6 degree-of-freedom
(or 3 degree-of-freedom in 2D) complex motions. Refer to the file
WINPOST.OUT for the entry frequency for each wave component.
WWBODY.VEL This file contains the velocity of the platform at each output time in the
time-domain simulation. Each line of the file contains the number of time
steps and 6 degree-of-freedom (or 3 degree-of-freedom in 2D) body
velocities.
WWBODY.FRC This file records external forces (diffraction force, viscous force, potential
force from convolution integral, and dynamic wind force) on the platform at
each output time (in every NINT time steps) in the time-domain simulation.
There are four lines of output for each time interval. The first line is the
diffraction force, the second line is the viscous force, the third line is the
potential force from convolution integral, and the fourth line is the dynamic
wind force. The data in the fourth line is just a reflection of the data read
from the file WINDF.IN.
17
The following output files are created for each leg (x in the file name represents the leg number)
LEGx.DIS
This file contains the nodal positions of the leg x at each static iteration or at
each output time in the time-domain simulation, or the amplitude (complex
number) of the nodal motion in the frequency-domain analysis. For each
step of static iteration or time-domain output, each line of the file contains
nodal number, nodal position vector and nodal tangential vector. In the
frequency-domain analysis, for each node, the data in the file contain the
number of wave components, the complex nodal motion vector, and the
complex nodal tangential vector. Refer to the file WINPOST.OUT for the
entry frequency for each wave component.
LEGx.FRC
This file contains the nodal reaction forces of the elements at each static
iteration or at each output time in the time-domain simulation, and the
complex amplitude of the nodal reaction force of the elements in the
frequency domain. At each step of static iteration or time-domain
integration, the output contains the following for each element: element
number and the nodal reaction force vector (Fx, Fy, Fz, Mx, My, Mz in global
coordinate system) at the first node; Element number and nodal reaction
force at the second node (with higher nodal number); Element number and
the total tension, total shear and total bending moment at the first node;
Element number and the total tension, total shear and total bending moment
at the second node. In the frequency-domain analysis, for each element, the
data contain the number of wave components, complex nodal reaction force
vector (Fx, Fy, Fz, Mx, My, Mz in global coordinate system) at the first node
and complex nodal reaction force at the second node; complex tension, shear
and bending moment at the first node and complex tension, shear and
bending moment at the second node. Refer to the file WINPOST.OUT for
the entry frequency for each wave component.
LEGx.TSN
This file contains all the nodal axial tensions at each iteration in the static
analysis, or at each output time in the time-domain simulation, or the
complex amplitude of the nodal tension in the frequency-domain analysis.
for each step of static iteration or time-domain output, each line of the data
contains nodal number and nodal tension. In the frequency-domain analysis,
for each node, the data contain the number of wave components and
complex nodal tension. Refer to the file WINPOST.OUT for the entry
frequency for each wave component.
LEGx.TTN
The file contains the nodal axial tension for the last node, which is connected
to the platform, at each output time in the time-domain simulation, or the
complex amplitude of the nodal tension for the last node in the frequencydomain analysis. In the time-domain simulation, each line of the file contains
the number of time steps and the tension. In the frequency-domain analysis,
the file contains the number of wave components and complex nodal
18
tension. Refer to the file WINPOST.OUT for the entry frequency for each
wave component.
19
5. EXAMPLES
In this manual, seven representative examples are included. They are selected to test various
functions of the program. They can also be used as a sample when users prepare a new input file.
The examples are explained in the following sections.
5.1 EXAMPLE 1: COUPLED TLP ANALYSIS (TIME DOMAIN)
In this example, a time-domain simulation is performed for an 8-leg, 4-column TLP (column
radius=7.62m, column draft=24.87m, column center-to-center distance=48.76m) in a 100-year
storm condition (JONSWAP with Hs=12.7m, Tp=14.9s, and overshoot parameter=2.4) with wave
heading=45 degrees. The water depth is 986m. The time series of the wave profile is automatically
generated inside the program and no dynamic wind force is applied (IFILE=0 in WINPOST.WV).
Total wave forces are applied (IPTW1=1) and the instantaneous added-mass correction for columns
is turned off (IPTW2=0). Eight wave frequencies (0.24 – 1.8 rad/s) are used as an entry to calculate
first- and second-order forces (QTF) and hydrodynamic coefficients. All the other values are
interpolated from them. The tethers are made of steel piles with 2 different sizes in diameter and
thickness (NMAT=2). To simplify the model, the 2 tethers at each column are clustered and
modeled as one leg with equivalent material and hydrodynamic properties. The legs are hinged both
to the sea floor and to the platform. In the analysis, the current profile is defined by users (see
CRPT in the second data group of WINPOST.WV), and a constant wind force on the platform is
applied through BUOY in the first data group of WINPOST.WV. A static analysis is performed
first with legs only, and second with hull/tether to set the system in a static equilibrium. Then, a
time-domain dynamic simulation is started with a time interval of 0.05 seconds and a duration of
4,500 seconds (90,000 time steps, with 5,000 steps for ramp).
20
The following is the input file WINPOST.IN:
3 4 2 9.8065 1025.0
100 90000 0.05 10
-983.285 1.E8
0. 0. 0.
NDIM,NLEG,NMAT,GRAVITY
MITER,NSTEP,DT,NINT
BOTTM,CB
BX(NIDM)
2.198E10 1.296E9 819.074 814.38 1628.76 728.98 0.0
2.802E10 1.620E9 1057.264 814.38 1628.76 728.98 0.0
GAE,GEI,GRHOL,GRHOA,GCI,GCD,GAS
GAE,GEI,GRHOL,GRHOA,GCI,GCD,GAS
11 1
29.05 29.05 -983.285
29.05 29.05 -20.605
NELEM,IFLAG1
PA(3)
PB(3)
86.920
86.920
86.920
86.920
87.857
87.857
87.857
87.857
87.857
87.857
87.857
0
0
0
0
0
0
0
0
0
0
0
2
2
2
2
1
1
1
1
1
1
1
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
(LEG 1)
RLEN,IOPTN,MAT,TZER
3
NBVP
1
1
1
1
2
3
1 29.05
1 29.05
1 -983.285
0
NBVS
0
2
2.0E13 2.0E13 2.0E13 0.0
0.0 0.0 1.0
29.05 29.05 -20.605
0
GSL,GSR,GE,GX
GDL
2
1 10
NOUT
NEOUT
11 1
29.05 -29.05 -983.285
29.05 -29.05 -20.605
NELEM,IFLAG1 (LEG2)
86.920
86.920
86.920
86.920
87.857
87.857
87.857
87.857
87.857
87.857
87.857
0
0
0
0
0
0
0
0
0
0
0
2
2
2
2
1
1
1
1
1
1
1
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
3
1
1
1
1
2
3
1 29.05
1 -29.05
1 -983.285
0
0
2
2.0E13 2.0E13 2.0E13 0.0
0.0 0.0 1.0
29.05 -29.05 -20.605
0
21
2
1 10
11 1
-29.05 -29.05 -983.285
-29.05 -29.05 -20.605
86.920
86.920
86.920
86.920
87.857
87.857
87.857
87.857
87.857
87.857
87.857
0
0
0
0
0
0
0
0
0
0
0
2
2
2
2
1
1
1
1
1
1
1
NELEM,IFLAG1 (LEG3)
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
3
1
1
1
1
2
3
1 -29.05
1 -29.05
1 -983.285
0
0
2
2.0E13 2.0E13 2.0E13 0.0
0.0 0.0 1.0
-29.05 -29.05 -20.605
0
2
1 10
11 1
-29.05 29.05 -983.285
-29.05 29.05 -20.605
86.920
86.920
86.920
86.920
87.857
87.857
87.857
87.857
87.857
87.857
87.857
0
0
0
0
0
0
0
0
0
0
0
2
2
2
2
1
1
1
1
1
1
1
NELEM,IFLAG1 (LEG 4)
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
1.717e7
3
1
1
1
1
2
3
1 -29.05
1 29.05
1 -983.285
0
0
2
2.0E13 2.0E13 2.0E13 0.0
0.0 0.0 1.0
-29.05 29.05 -20.605
0
2
1 10
1
0
1
0
0
0 1e-8
IPT1,IPT2,IPT3,IPT4,TOLERANCE ( FIND EQUILIBRIUM FOR LEG ONLY)
22
0
1
1
0
0
0
1 1e-8
IPT1,IPT2,IPT3,IPT4,TOLERANCE ( FIND EQUILIBRIUM FOR COUPLE SYSTEM)
1
0
1 5000
IPT1,IPT2,IPT3,IPT4,NRAMP (TIME DOMAIN SIMULATION)
-------------------input file for TLP
--------------------
The following is the input file WINPOST.WV
8
0.4400
1
0.78540E+00
0.2400
0.19182E+08
0.00000E+00
0.00000E+00
0.00000E+00
-0.25340E+09
0.00000E+00
...
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.6398
0.8400
0.00000E+00
0.19182E+08
0.00000E+00
0.25340E+09
0.00000E+00
0.00000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
(number of frequency)
1.2393 1.4996 1.8003
(number of heading)
1.0403
0.00000E+00
0.00000E+00
0.14669E+08
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00 -0.25340E+09
0.25340E+09 0.00000E+00
0.00000E+00 0.00000E+00
0.10404E+11 0.00000E+00
0.00000E+00 0.10404E+11
0.00000E+00 0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
0.00000E+00
0.17622E+11
0.0000E+00 0.0000E+00 0.0000E+00
0.0000E+00 0.0000E+00 0.0000E+00
0.7334E+07 0.0000E+00 0.0000E+00
0.0000E+00 -0.6761E+08 0.0000E+00
0.0000E+00 0.0000E+00 -0.6761E+08
0.0000E+00 0.0000E+00 0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
(BSTIFF)
0.1901E+08 0.0000E+00
0.0000E+00 0.1901E+08
0.0000E+00 0.0000E+00
0.0000E+00 -0.7707E+08
0.7707E+08 0.0000E+00
0.0000E+00 0.0000E+00
0.0000E+00 0.0000E+00
0.0000E+00 -0.7707E+08
0.1901E+08 0.0000E+00
0.0000E+00 0.1847E+11
0.0000E+00 0.0000E+00
0.0000E+00 0.0000E+00
0.7707E+08
0.0000E+00
0.0000E+00
0.0000E+00
0.1930E+11
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.0000E+00
0.1681E+11
(BMASS)
1.7225E+06
0.6987E+08 -6.9828E+06
6.9828E+06
0.0000E+00
(BUOY)
1.7225E+06
(THE ABOVE DATA ARE CREATED BY WINTCOL, AND BUOY IS MODIFIED TO INCLUD STEADY WIND FORCE ON TLP))
12.71 14.9 2.4 45 0.15 1.2 0 45 986.333
41 1 0 -2000
(HS,TP,GAMA,BETAWV,FREMIN,FREMAX,VC,BETAC,DEPTH)
(NFRESP,NHDSP,NSPREAD,IRAND)
0
0
(NFRE2D)
(NFRE2S)
4
(NCPREL)
0.000
-57.912
-83.820
-986.333
1.280
1.280
0.000
0.000
(CRPT(2))
0
(IFILE)
1
(IPTW1)
8
(NTRUS)
24.384
-24.384
-24.384
24.384
24.384
-24.384
-24.384
24.384
24.384
24.384
-24.384
-24.384
24.384
24.384
-24.384
-24.384
20 24.384 24.384 -24.872 0 0
20 -24.384 24.384 -24.872 0 0
20 -24.384 -24.384 -24.872 0 0
20 24.384 -24.384 -24.872 0 0
-24.872 -24.384 24.384 -24.872
-24.872 -24.384 -24.384 -24.872
-24.872 24.384 -24.384 -24.872
-24.872 24.384 24.384 -24.872
0
4.843e3 1
4.843e3 1
4.843e3 1
4.843e3 1
0 0 4.218E3
0 0 4.218E3
0 0 4.218E3
0 0 4.218E3
(column)
0
0
0
0
(pontoon)
(nplat)
23
-------------------TLP, WINTCOL RESULTS
--------------------
24
5.2 EXAMPLE 2: COUPLED TLP ANALYSIS (TIME-DOMAIN ANALYSIS)
In this example, the time-domain simulation is performed for the same TLP introduced in Example
1 with user-defined input wave components. The input file “WCOMP.IN” needs to be prepared
for this example. When the wave frequency, wave amplitude and phase in WCOMP.IN are the
same as those generated by the program in Example 1 (see the WINPOST.OUT file of Example 1),
the results of the simulation should be identical to those of Example 1, which is a way to verify the
present option. The only modification needed in the input file is to change the parameter IFILE
located at the end of WINPOST.WV to 2 (It was 0 in Example 1).
25
5.3 EXAMPLE 3: UNCOUPLED TETHER ANALYSIS (TIME-DOMAIN ANALYSIS)
In this example, the uncoupled time-domain simulation is performed for the four legs of the TLP of
Example 1. In the simulation, the upper (second) ends of legs are hinged to and move with the
platform, of which the motion is pre-defined in the optional file “WBODY.IN”. To verify this
option, the Example 1 is run again with NINT=1 (output the results for every time step), and the
resulting output file WWBODY.DIS can be modified to create WBODY.IN. Then, run the
program again with WBODY.IN. The results of the simulation should be identical to those of
Example 1.
The input file WINPOST.IN is the same as that of Example 1, except the following run-time
command:
...
1
0
1
1
0
0
0
0 1e-8
IPT1,IPT2,IPT3,IPT4,TOLERANCE ( FIND EQUILIBRIUM FOR LEG ONLY)
1
0
0 5000
IPT1,IPT2,IPT3,IPT4,NRAMP (TIME DOMAIN SIMULATION, LEG ONLY)
-------------------input file for TLP
--------------------
The file WINPOST.WV can be changed as follows:
12.71 14.9 2.4 45 0.15 1.2 0 45 986.333
41 1 0 -2000
(HS,TP,GAMA,BETAWV,FREMIN,FREMAX,VC,BETAC,DEPTH)
(NFRESP,NHDSP,NSPREAD,IRAND)
0
0
(NFRE2D)
(NFRE2S)
4
0.000
-57.912
-83.820
-986.333
(NCPREL)
1.280
1.280
0.000
0.000
(CRPT(2))
0
(IFILE)
1
(IPTW1)
0
(NTRUS)
0
(nplat)
-------------------TLP, WINTCOL RESULTS
--------------------
26
5.4 EXAMPLE 4: COUPLED TLP ANALYSIS IN FREQUENCY DOMAIN
In this example, a frequency-domain analysis is performed for the same TLP of Example 1. In the
file WINPOST.IN, all the input data are the same as those used in the time-domain analysis except
the following run-time command:
...
1
0
1
0
1
0
1
-1
1
0
1
-1
0
0
0
0 1e-8
IPT1,IPT2,IPT3,IPT4,TOLERANCE ( FIND EQUILIBRIUM FOR LEG ONLY)
0
0
1 1e-8
IPT1,IPT2,IPT3,IPT4,TOLERANCE ( FIND EQUILIBRIUM FOR COUPLE SYSTEM)
1
0
1 1e-8
(FIND MEAN POSITION OF COUPLE SYSTEM IN CURRENT AND DRIFT FORCE)
1
2
1
0
0
0
1 1e-3
1 1e-6
1 1e-3
(FREQUENCY DOMAIN ANALYSIS AT THE MEAN POISITON)
(FIND MEAN POSITION USING LIEARIZED MEAN DRAG AND DRIFT FORCE)
(RE-DO THEFREQUENCY DOMAIN ANALYSIS AT THE NEW MEAN POISITON)
-------------------input file for TLP
--------------------
The frequency-domain analysis is a user-controlled iterative process. First, a mean position is
estimated based only on current and drift forces. Then a frequency-domain analysis is performed at
the mean position. In the frequency-domain analysis, the linearized mean drag forces, which include
both current and mean wave drag forces, are computed. Then the static analysis is performed again
using the linearized mean drag forces to compute a more accurate mean position of the system,
which is followed by another frequency-domain analysis for the new mean position. By using the
run-time command, users control the number of iterations of the static/frequency domain analyses
to obtain accurate mean and frequency domain results. It is recommended that at least one iteration
be needed in the frequency-domain analysis.
The input file WINPOST.WV is the same as that used in Example 1 except that low- and highfrequency components near the natural periods of the platform are added to the file:
...
12.71 14.9 2.4 45 0.15 1.2 0 45 986.333
41 1 0 1
(HS,TP,GAMA,BETAWV,FREMIN,FREMAX,VC,BETAC,DEPTH)
(NFRESP,NHDSP,NSPREAD,IRAND)
7
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.12
7
1.55 1.6 1.65 1.7 1.75 1.8 1.85
(NFRE2D)
4
(NCPREL)
0.000
-57.912
-83.820
-986.333
1.280
1.280
0.000
0.000
(NFRE2S)
(CRPT(2))
0
(IFILE)
1
(IPTW1)
8
(NTRUS)
24.384 24.384 20 24.384 24.384 -24.872
-24.384 24.384 20 -24.384 24.384 -24.872
-24.384 -24.384 20 -24.384 -24.384 -24.872
0 0 4.843e3 1
0 0 4.843e3 1
0 0 4.843e3 1
27
24.384 -24.384 20 24.384 -24.384 -24.872 0 0 4.843e3 1
24.384 24.384 -24.872 -24.384 24.384 -24.872 0 0 4.218E3
-24.384 24.384 -24.872 -24.384 -24.384 -24.872 0 0 4.218E3
-24.384 -24.384 -24.872 24.384 -24.384 -24.872 0 0 4.218E3
24.384 -24.384 -24.872 24.384 24.384 -24.872 0 0 4.218E3
0
(column)
0
0
0
0
(pontoon)
(nplat)
-------------------TLP, WINTCOL RESULTS
--------------------
28
5.5 EXAMPLE 5: COUPLED SPAR ANALYSIS IN TIME DOMAIN
In this example, a time-domain simulation is performed for a SPAR platform. The SPAR has the
same dimension as that used in the JIP experiments conducted in the OTRC wave basin. The SPAR
has a diameter of 40.50 meters and a draft of 198.12 meters. The water depth is 780 meters. As a
particular design condition, it is assumed that the SPAR is positioned by four groups of catenary
mooring lines with 3 lines in each group. In the analysis, each group of lines is modeled by a single
catenary mooring line with equivalent material and hydrodynamic properties. The mooring lines
have a chain-wire-chain combination (3 material types in the analysis) and are hinged at the sea floor
and fair-leaders. The current profile is defined by the user (in this example, a linearly decaying shear
current is used). In the simulation, the time interval is 0.05 seconds and the length of the simulation
is 45,00 seconds (90,000 time steps, with 5,000 steps for ramping).
The static equilibrium for the mooring lines without considering the platform is first computed in
the analysis. The ends of the mooring lines at the fair-leaders are assumed to be connected to a fixed
boundary in the uncoupled analysis. The purpose of the preliminary static analysis is to put the
mooring lines in the actual catenary shaped position. Then, a static equilibrium is reached for the
coupled platform-mooring system and it is ready to start the time-domain simulation for the coupled
system.
29
The following is the input file WINPOST.IN:
3 4 3 9.8065 1025.0
100 90000 0.05 10
-1780.0 1.E8
0. 0. 0.
NDIM,NLEG,NMAT,GRAVITY,RHOW
MITER,NSTEP,DT,NINT
BOTTM,CB
BX(NIDM)
1.7001E9 0.0 1326.749 169.059 338.117 332.100 0.0
4.8276E9 0.0 360.149 68.457 136.915 307.539 0.0
1.5981E9 0.0 1326.749 169.059 338.117 332.100 0.0
GAE,GEI,GRHOL,GRHOA,GCI,GCD,GAS
GAE,GEI,GRHOL,GRHOA,GCI,GCD,GAS
GAE,GEI,GRHOL,GRHOA,GCI,GCD,GAS
13 1
MOORING LINE 1
-790.0 0.0 -780.0
-20.5 0.0 -106.7
NELEM,IFLAG1
PA(3)
PB(3)
30.48
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
45.72
45.72
0
0
0
0
0
0
0
0
0
0
0
0
0
3
2
2
2
2
2
2
2
2
2
2
1
1
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
RLEN,IOPTN,MAT,TZER
3
NBVP
1
1
1
1
2
3
1 -790
1 0.0
1 -780
0
NBVS
0
2
5.0e12 5.0e12 5.0e12 0.0
0.0 0.0 1.0
-20.5 0.0 -106.7
0
GSL,GSR,GE,GX
GDL
2
1 13
NOUT
NEOUT(NOUT)
13 1
MOORING LINE 2
0.0 -790.0 -780.0
0.0
-20.5 -106.7
30.48
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
45.72
45.72
0
0
0
0
0
0
0
0
0
0
0
0
0
3
2
2
2
2
2
2
2
2
2
2
1
1
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
3
NBVP
1
1
1
1
2
3
1 0.0
1 -790
1 -780
0
NBVS
0
2
30
5.0e12 5.0e12 5.0e12 0.0
0.0 0.0 1.0
0.0 -20.5 -106.7
0
2
1 13
13 1
MOORING LINE 3
790.0 0.0 -780.0
20.5 0.0 -106. 7
30.48
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
45.72
45.72
0
0
0
0
0
0
0
0
0
0
0
0
0
3
2
2
2
2
2
2
2
2
2
2
1
1
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
3
NBVP
1
1
1
1
2
3
1 790
1 0.0
1 -780
0
NBVS
0
2
5.0e12 5.0e12 5.0e12 0.0
0.0 0.0 1.0
20.5 0.0 -106.7
0
2
1 13
13 1
0.0
0.0
MOORING LINE 4
790.0 -780.0
20.5 -106.7
30.48
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
91.80
45.72
45.72
0
0
0
0
0
0
0
0
0
0
0
0
0
3
2
2
2
2
2
2
2
2
2
2
1
1
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
7.0E5
3
NBVP
1
1
1
1
2
3
1 0.0
1 790
1 -780
0
NBVS
0
2
5.0e12 5.0e12 5.0e12 0.0
0.0 0.0 1.0
0.0 20.5 -106.7
0
31
2
1 13
1
0
1
0
1
1
0
0
0
0 1e-6
IPT1,IPT2,IPT3,IPT4,TOLERANCE ( FIND EQUILIBRIUM FOR LEG ONLY)
0
0
1 1e-6
IPT1,IPT2,IPT3,IPT4,TOLERANCE (FIND EQUILIBRIUM FOR COUPLED SYSTEM)
1
0
1 5000
IPT1,IPT2,IPT3,IPT4,NRAMP (TIME DOMAIN SIMULATION)
------------------------input file for fat spar
-------------------------
The following is the input file WINPOST.WV
...
0.0000E+00
0.0000E+00
0.2000E+08
0.0000E+00 0.0E+00
0.0000E+00
(BUOY)
(THE ABOVE DATA ARE CREATED BY WINTCOL)
13.11 14.0 2.0 0.0 0.15 1.2 0 0.0 780
51 1 0 -2000
(HS,TP,GAMA,BETAWV,FREMIN,FREMAX,VC,BETAC,DEPTH)
(NFRESP,NHDSP,NSPREAD,IRAND)
0
0
(NFRE2D)
(NFRE2S)
3
(NCPREL)
0.0 1.31
-107.7 0.0
-780.0 0.0
(CRPT(2))
0
(IFILE)
5
(IPTW12)
1
0
(NTRUS)
0 20. 0
0 -198.12
0
0 0 1.25e4 1
(nplat)
--------------------SPAR, WINTCOL RESULTS
---------------------
32
5.6 EXAMPLE 6: CATENARY
This example is for a static catenary analysis to verify the static-iteration formulation. The catenary
is hinged at one end (with essential BC), and is subjected to a horizontal force at the other end (with
natural BC). The applied force is equal to the weight of the catenary. Ten equally spaced elements
are used in the static analysis. The initial position of the line is set to be horizontal. The program
computes the equilibrium position of the line and nodal reaction forces. Only one input file
WINPOST.IN is needed for this computation. If users want to test the catenary with a possibility
of touching a foundation, one only needs to change the parameter IOPTN of each element to 1.
The following is the input file WINPOST.IN for this example:
3 1 1 9.8065 1025.0
100 1000 0.05 10
-0.30 1.E8
0. 0. 0.
NDIM,NLEG,NMAT,GRAVITY,RHOW
MITER,NSTEP,DT,NINT
BOTTM,CB
BX(NIDM)
1E10 0.0 0.1019732 0.0 1.0 1.0 0.0
GAE,GEI,GRHOL,GRHOA,GCI,GCD,GAS
10 0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
NELEM,IFLAG1 (LEG 1)
R(3),RP(3),TZER
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0
0
0
0
0
0
0
0
0
0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1
1
1
1
1
1
1
1
1
1
RLEN,IOPTN,MAT,
3
NBVP
1
1
1
1
2
3
1
1
1
0.
0.
0.
1
11
1
1
1.
NBVS
0
0
NEND1
NEND2
2
1 10
NOUT
NEOUT
1
0 0 0 0 1e-8
1
0 0 1 0 1e-8
0
----------------------input file for CATENARY
-----------------------
IPT1,IPT2,IPT3,IPT4,TOLERANCE (FIND EQUILIBRIUM; EXTENSIBLE)
IPT1,IPT2,IPT3,IPT4,TOLERANCE (FIND EQUILIBRIUM; INEXTENSIBLE)
33
5.7 EXAMPLE 7: PENDULUM VIBRATION
This dynamic-analysis example is for the large-amplitude motion of a bar-pendulum in the air. This
example is selected to verify the dynamic formulation of the program. The uniform rigid bar was
modeled by ten elements with a very large bending and stretching stiffness. A similar example is
also given in Garrett (1982). The bar is hinged at one end and released from rest in a horizontal
position at time t=0. The motion is computed using a time step of 0.01s, which is very small since
the motion is extremely nonlinear. Only WINPOST.IN is needed for this computation.
3 1 1 9.8065 1025.0
100 1000 0.01 1
-0.30 1.E8
0. 0. 0.
NDIM,NLEG,NMAT,GRAVITY,RHOW
MITER,NSTEP,DT,NINT
BOTTM,CB
BX(NIDM)
1E10 1E10 1.0 0.0 1.0 1.0 0.0
GAE,GEI,GRHOL,GRHOA,GCI,GCD,GAS
10 0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
NELEM,IFLAG1 (LEG 1)
R(3),RP(3),TZER
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0
0
0
0
0
0
0
0
0
0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1
1
1
1
1
1
1
1
1
1
RLEN,IOPTN,MAT
3
NBVP
1
1
1
1
2
3
1
1
1
0.
0.
0.
0
0
0
NBVS
NEND1
NEND2
2
1 10
NOUT
NEOUT
1
1 0 0 0 0
IPT1,IPT2,IPT3,IPT4,TOLERANCE
0
----------------------input file for CATENARY
-----------------------
34
REFERENCES
Garrett, D. L., (1982), “Dynamic Analysis of Slender Rods,” ASME Journal of Energy Resources
Technology, Vol. 104, pp. 302-306
Nordgren, R. P., (1974), “On Computation of the Motion of Elastic Rods,” ASME Journal of
Applied Mechanics, Sept. pp. 777-780.
Kim, M.H. (1992), “Difference-frequency wave loads on a large body in multi-directional waves”, J.
of Applied Ocean Research, Vol.14, No.6, 353-370.
Newman, J.N. (1974), “Second-order slowly-varying forces on vessels in irregular waves”, Symp. on
Dynamics of Marine Vehicles and Structures in Waves, London.
Ran, Z., Kim, M.H., Niedzwecki, J.M. & Johnson, R.P. (1996), “responses of a spar platform in
random waves and currents (Experiment vs. Theory)”, International Journal of Offshore and Polar
Engineering (In Press).
Ran, Z., Kim, M.H., (1996), “Nonlinear Coupled Responses of a Tethered Spar Platform in Waves”,
Proceedings of the Sixth International Offshore and Polar Engineering Conference, Vol. 1, pp281288.
Rodenbusch, G., Garrett, D. L., and Anderson, S. L. (1986), “Statistical Linearization of VelocitySquared Drag Forces, “Proceedings of the Fifth OMAE Symposium, Tokyo, Vol. 1, pp. 123-129.
Sarpkaya, T (1986), “force on a circular cylinder in viscous oscillatory flow at low Keulega-Carperter
number,” Journal of Fluid Mechanics, Vol 165, pp 61-71.
35
APPENDIX I: The First Input-Data-Group of WINPOST.WV
The input file WINPOST.WV consists of two groups of data. The first group is for the
hydrodynamic information of the platform. If the program WINTCOL is used to compute
hydrodynamics for the platform, it will automatically generate the first group of WINPOST.WV.
Users only need to prepare the second group of input data starting at the end the first group. The
second group of input data was described in Section 3.2. All the input data in WINPOST.WV are
defined in the rigid-body (platform) coordinate system. If WINTCOL is not used, users need to
prepare the first group of data in the following format:
NFRE
FREQT1, ... , FREQTNFRE
NHD
HEADT1, ... , HEADTNFRE
RINER1
...
RINERNFRE
DAMP1
...
DAMPNFRE
WF11,1
...
WF1NHD,NFRE
WDD1,1
...
WDDNHD,NFRE
WF2D1,1,1,1
...
WF2DNHD,NHD,NFRE,NFRE
WF2S1,1,1,1
...
WF2SNHD,NHD,NFRE,NFRE
BSTIFF
BMASS
BOUY
NCLMN
XCLMN11, XCLMN21, XCLMN31,RCLMN 1
36
...
XCLMN1NCLMN, XCLMN2 NCLMN, XCLMN3 NCLMN, RCLMN NCLMN
In this group, NFRE is the total number of frequencies used in the hydrodynamic calculation, and
FREQT is the wave frequency (rad/s). The wave frequencies should be in an increasing order.
NHD is the total number of wave headings used in the hydrodynamic calculation, and HEADT is
the wave heading (rad). The values of the wave headings should be in an increasing order and in the
range from -/2 to /2 with respect to the main direction. RINERn is the 66 added mass matrix
of the n-th frequency, and DAMPn is the 66 wave damping matrix of the n-th frequency. WF1I,J is
the linear wave force transfer function(LTF) for frequency J in I heading. It is a complex vector
with 6 degrees of freedom(surge, sway, heave, roll, pitch, yaw). The format of WF1 is defined as
follows:
Loop I from 1 to NHD
Loop J from 1 to NFRE
Read 6-degree-of-freedom force vector WF1I,J (complex)
End loop J
End loop I
WDDI,J is the wave drift damping coefficient for frequency J in I heading I. It is a real vector with 6
degrees of freedom. The format for WDD is defined as follows:
Loop I from 1 to NHD
Loop J from 1 to NFRE
Read 6-degree-of-freedom drift damping coefficient WDDI,J (real)
End loop J
End loop I
WF2DI,J,K,L is the difference-frequency wave force quadratic transfer function (QTF) for
frequencies K, L and wave headings I, J, respectively. It is a complex vector with 6 degrees of
freedom. The format for WF2D is defined as follows:
Loop I from 1 to NHD
Loop J from 1 to NHD
Loop K from 1 to NFRE
Loop L from K to NFRE
Read 6-degree-of-freedom difference-frequency QTFs WF2DI,J,K,L (complex)
End loop L
End loop K
End loop J
End loop I
Similarly, the WF2SI,J,K,L is the sum-frequency QTF for frequencies K, L and wave headings I, J,
respectively. It is a complex vector with 6 degrees of freedom. The order of the input data for WF2S
is defined as follows:
37
Loop I from 1 to NHD
Loop J from 1 to NHD
Loop K from 1 to NFRE
Loop L from K to NFRE
Read 6-degree-of-freedom sum-frequency QTFs WF2SI,J,K,L (complex)
End loop L
End loop K
End loop J
End loop I
BSTIFF is a 66 restoring stiffness matrix for the platform. The restoring force usually comes only
from hydrostatics since the mooring system is modeled explicitly in the coupled analysis. In an
uncoupled analysis (for platform only) without using WINPOST, user needs to include the
contributions of the mooring system in BSTIFF. BMASS is the 66 mass matrix of the platform.
BOUY is the 6-degree-of-freedom force vector (real) and indicates the net external force (including
buoyancy force) acting on the platform. For example, the 3rd component in BOUY (net heave
force= weight-buoyancy) is equal to the total pretension in the tendon in a coupled TLP analysis,
and is zero in an uncoupled analysis. Users can also include other external force such as constant
wind forces in BOUY. NCLMN is the total number of vertical columns of the platform.
XCLMN1n and XCLMN2 n are the x and y coordinate of the axis of the n-th column, respectively.
XCLMN3n is the draft (with negative sign)of the n-th column. RCLMNn is the radius of the n-th
column.
38
APPENDIX II: The wind force generation program WIND1.FOR
The program WIND1.FOR generates time series of wind forces on the rigid body (floating
platform). The wind force time series is then used as an input for program WINPOST if the
dynamic wind force is desired in the time domain simulation. The dynamic wind velocity is
computed based on the API wind spectrum (API RP 2A-WSD, Section 2.3.2) or NPD wind
spectrum
Users need to prepare a input file for the program. The input file shall be named “WIND.IN”, and
the data in the file is listed as follows
NFLAG,V10,BETA,PERI1,PERI2,NPERI,PEAK,RHOW,ISEED
DT,NSTEP
NAREA
AREA1,AX1,AY1,AZ1,DRAG1
……
AREANAREA,AXNAREA,AYNAREA,AZNAREA,DRAGNAREA
Where the NFLAG is 0 for SI unit system and is 1 for US unit system. V10 is the one hour mean
wind speed at the reference elevation of 10 meters (33 feet). BETA is the wind direction (where
wind goes to) in degrees. PERI1 and PERI2 are the minimum and maximum wind periods,
respectively, defined for the conversion of wind spectrum into harmonic wind components. NPERI
is the total number of wind components. PEAK is the peak coefficient for API spectrum. It is
defined in API rules (RP 2A, equation 2.3.2-7). The value of PEAK ranges from 0.01 to 0.10, and
commonly a value of 0.025 is suggested. If NPD spectrum is used to compute dynamic wind
force, Users shall gave a negative value to PEAK. RHOW is the density of the air. ISEED is the
random seed which is used to generate random phases for the wind components. It shall be a
negative integer. DT and NSTEP are the time interval and total time steps, respectively, for the
wind force time series generation. The DT shall be the same as the time interval used in program
WINPOST, and the total time step (NSTEP) shall be equal or larger than the total time step in
WINPOST. NAREA is the total number of objects on the platform that subject to wind force. For
each object, users need to input: AREA—area of the object normal to the wind; AX,AY,AZ—
position of the pressure center of the object. The platform coordinate system shall be same as that
used in the WINDPOST (origin shall on the mean water line) ; DRAG—drag coefficient. If there
is no more accurate method such as model test to determine the value, the drag coefficient can be
computed by the formula: DRAG=1.0(shape coefficient), where the shape coefficient is define in
API rules (RP 2A section 2.3.2e). In the program, the wind force on the object is computed by the
following formula: wind force = (1/2)PHOWAREADRAG (wind velocity at pressure
center)2.
The program generates two output files: 1) WIND.OUT consists of the echo of the input and the
statistics (mean and standard deviation) of the generated wind force time series: 2) WINDF.IN is
the wind force time series. Each line in the file consists of wind forces and moments in the
following order: surge force, sway force, heave force, roll moment, pitch moment, yaw moment.
The file WINDF.IN can be used as an input file for program WINPOST without any
modification.
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