aqwa-intro 14.5 l03 aqwa suite
DESCRIPTION
Aqwa-Intro 14.5 L03 Aqwa SuiteTRANSCRIPT
© 2012 ANSYS, Inc. May 8, 2013 1 Release 14.5
14.5 Release
Lecture 03
ANSYS Aqwa Suite
© 2012 ANSYS, Inc. May 8, 2013 2 Release 14.5
A. Core Aqwa Programs
Aqwa-Line • 3-D diffraction & radiation analysis program for wave force
and structure response calculations; hydrostatic analysis
Aqwa-Librium • Structure equilibrium position and force balance
calculations; eigen-mode and dynamic stability analysis
Aqwa-Fer • Spectral analysis of structure motion (wave frequency
or/and drift frequency) and mooring tension in irregular waves
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... Core AQWA Programs
Aqwa-Naut • Time domain program for wave frequency structure motion
and mooring tension analyses in regular and irregular waves
Aqwa-Drift • Time domain program for drift frequency and wave
frequency structure motion and mooring tension analysis in irregular waves
Aqwa Graphical Supervisor (AGS) • AQWA pre and post processor; on-line analysis
© 2012 ANSYS, Inc. May 8, 2013 4 Release 14.5
Librium
ANSYS
Mechanical AGS
Fer Naut Drift
Line
EXCEL
…Core Aqwa Programs
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B. AGS AQWA Graphical Interface can be used to;
• Generate Mesh (for ship shape models)
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AQWA Graphical Supervisor AQWA Graphical Interface can be used to;
• Post process
• Force & Response Curves
• Shear Force & Bending Moment
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AQWA Graphical Supervisor AQWA Graphical Interface can be used to;
• Post process
– Pressure Contours
– Wave Surface Contours
– Diffracted Wave Surface
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AQWA Graphical Supervisor
AGS Interface Overview
File - Open/close, and save AQWA models
Edit - Create and edit AQWA models
Run - Perform an AQWA analysis on the presently loaded model
Graphs - Display and manipulate AQWA results graphically
Plots - Display and edit AQWA models visually
Cable Dynamics - Define and analyze problems involving cable dynamics
Help - Access to the online help system
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AGS File Handling
The File Menu provides access to open any of the standard AQWA files
These files will be discussed in detail later in this training session
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AGS Database Review
Provides access to data and results stored on the AQWA database. Note that, in general, it is NOT recommended to change data using this interface.
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AGS Analysis •Allows analyses to be run interactively.
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AGS Graphs Allows graphical plotting of frequency and time domain information
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AGS Model Visualization
Provides geometry and results presentation
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AGS Model Visualization
View Centre provides model
shift/pan facilities Position model origin at
center of screen
Enter
coordinates of a
point that will be
positioned at
center of screen.
Select Plot to
update the view
Can also shift/pan
by clicking on the
point on the model
that is required to
be plotted at the
center of the
screen
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AGS Model Visualization
View angle provides rotation
of model view
Rotations about screen Z
axis Rotations about screen X
axis
Current View Angle
Angle increment
C 30 degrees
M 10 degrees
F 1 degree
Isometric view
Elevations along X, Y, Z axes
Direction of view controlled
by + or – radio button
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AGS Model Visualization
Zoom buttons provide zoom
in/out facilities Size to screen
Zoom in +/out -
Zoom increment
C Coarse
F Fine Current View Size
Can also zoom
in/out by left
mouse button
“rubber band” on
image
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AGS Model Visualization
For analyses with multiple structures we can
select/de-select which are visible using the
colored check boxes at the bottom of the
visualization window
These boxes determine which
structures are visible. Red
indicates visible, white is not
visible. Click on box to
change status
Only one of these boxes will be
selected at any time. They
indicate which structure the
position information relates to
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AGS Wave Contours
Allows for 2-dimensional wave surface contours to be plotted following an Aqwa-Line analysis
Wave directions and frequencies are accessed using an index number, rather than the specific values required. This index number is specified as part of the input data to Aqwa-Line
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AGS Cable Dynamics Allows for additional processing and visualization of mooring line cable dynamics
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C. AQWA Suite need to knows
File names
File types
Deck system
Restart stages
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...AQWA Suite need to knows
AQWA File Names
• Every AQWA file name has two parts:
• run identifier (should be <= 28 characters) - a name to identify the run
• file extension to identify the type of file (e.g. *.dat, *.lis, *.res)
• A file name typically looks like;
• tanker.dat (input data)
• tanker.lis (output list file) etc...
• Each AQWA run involves several files
• The names of the run files (input/output) differ only in extension!
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...AQWA Suite need to knows Input/Output Files
• *.dat input data file (ASCII, LBDNF) • *.lin input file for AGS mesh generator (ASCII) • *.sfm input mass distribution for splitting forces (ASCII, AGS) • *.wht a wave height time history (ASCII, D) • *.wvt a wind velocity time history, no card needed (ASCII, DN) • *.xft an external force time history, no card needed (ASCII, DN) • *.mor mooring description file (ASCII, BDNF) • *.res restart file (binary, LBDNF) • *.hyd hydrodynamics file (binary, L) • *.eqp equilibrium position file (binary, B) • *.uss source strength file (binary, L) • *.pot potential file (binary, L) • *.mes output message file (ASCII, LBDNF) • *.lis output listing file (ASCII, LBDNF) • *.pos output position file (binary, DN) • *.plt output graphic file (binary, LBDNF) • *.pac pressures at centroids (binary, L) • *.vac velocities at centroids (binary, L)
See Aqwa-Ref 1.3 for details
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...AQWA Suite need to knows Input data (*.dat) file
• ASCII text file containing all the input data necessary for the Stages of Analysis about to be executed.
• in FIXED FORMAT and must be entered using a text editor.
• an editor that indicates the column & line no. of the current cursor position is highly recommended !!!
*.dat file format
• Most input data should be typed into the required columns !!!
• See Aqwa-Reference Chapter 4 for details
JOB MESH LINE
TITLE MESH FROM LINES PLANS/SCALING
OPTIONS REST END
RESTART 1 2
4col 4col5cols5cols 10 cols 10 cols 10 cols
01 COOR
01 1 45.000 -45.000 0.000
END01 999 0.000 0.000 -10.620
Column 21
02 ELM1
02QPPL DIFF 0(1)( 1)( 2)( 12)( 11)
06FREQ 1 6 0.10472 0.15708 0.25133 0.41888 0.52360
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...AQWA Suite need to knows
This is a binary file,
Written by all the AQWA programs
• Contains database associated with all the Stages of analysis which have so far been executed.
Typical information that can be contained on the .res file include:
• model definition
• hydrodynamic database
• main analysis parameters
Restart File (.res)
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...AQWA Suite need to knows
Comparison of .RES and .HYD (after Aqwa-Line solution)
Hydrodynamic File (.hyd)
• This is a binary file,
• Created by Aqwa-Line after diffraction/radiation analysis
• Contains a copy of the hydrodynamic database that is also stored on the Restart file
• Used in model manipulation (discussed in following workshops)
Restart File (.res) Hydrodynamic File (.hyd)
Data Stored Model definition Hydrodynamic database
Hydrodynamic database
Used For Additional analyses AGS Regenerating .hyd file
Additional analyses Data manipulation
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...AQWA Suite need to knows
This is a binary file,
Created during a solution stage
Contains either
• Forces and responses as a function of frequency
• Time history of forces and motions
• Positions and forces during iteration towards equilibrium
Used by the AGS
Graphical Plot File (.plt)
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...AQWA Suite need to knows
Deck system (now referred to as Data Category)
• AQWA Data (.dat) file has a predetermined deck system
• Each deck begins with a header, and terminates with an END statement, with the associated data defined between these statements
01 COOR
01 1 45.000 -45.000 0.000
01 999 0.000 0.000 -10.620
END
• Further explained later and in Workshops!!
Deck # Description
0 Overall administration parameters
1 Node coordinates
2 Element definitions
3 Material properties
4 Geometric properties
5 Global constants
6 Wave frequency and directions
7 Hydrodynamic properties
8 Drift force coefficients
9 Drift motion parameters
10 Hull drag coefficients
11 Environmental parameters
12 Constraints
13 Spectral/Regular wave parameters
14 Mooring line definitions
15 Starting conditions
16 Time integration/Iteration parameters
17 Additional hydro parameters for tubes
18 Printing options
19/20 Reserved for future use
21 Element and nodal loads
Deck header
Deck terminator
Data
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...AQWA Suite need to knows RESTART Stages
• Categorize analysis procedures
• Can be run individually or in combination with each other
• Data transfer is done between stages
* Calculation Stage Only
STAGE # FUNCTION/DEFINITION RELEVANT DECKS
1 Model Definition 1 to 5
2 Hydrodynamic coefficient database 6 to 8
3 Diffraction/Radiation analysis (L)* -
4 Main analysis parameters 9 to 20
5 Main analysis (BFDN)* -
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D. Aqwa-Line
Introduction
• Aqwa-Line is a 3D diffraction and radiation analysis program
• Frequency domain
• Structures are described by a number of panels
• Source distribution approach (boundary integration method)
• A source is placed at the centre of each panel and then the program solves for the source strengths, subject to the boundary conditions (details are addressed in Lecture 2 and AQWA Theory Manual)
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...Aqwa-Line
Features
• Removal of irregular frequencies by auto-generated lid
• Multi-body hydrodynamic interactions (lid to suppress standing waves)
• Forward speed
• Second order forces
• Mean drift forces:
• Far field momentum theory
• Near field pressure-motion integration method
• Full QTF matrix (difference & sum frequency components)
Aqwa-Line provides hydrodynamic coefficients for use in other programs in the AQWA suite
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...Aqwa-Line
General Warnings
Requirements Reason
Number of diffracting elements should be no more than 12k
Solution time
Maximum number of total elements is 18k
Solution time
Normals point out Modelling Convention
No gaps in between panels Force balance
Facets cannot cut surface Solution requirement
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...Aqwa-Line
Geometric Property Warnings
• Area ratio of adjacent elements < 3
• Aspect ratio (AR) > 1/3, where
(C = 1 for quadrilateral elements,
C = 2.3 for triangular elements)
• Element centres must be at least one facet radius (rf) apart,
• Shape factor (parameter for regularity of panel)
• <0.2 = warning
• <0.02 = fatal error
• See AQWA Theory Manual for more detail
Csidelongest
areaAR .
2
arear f
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...Aqwa-Line Hydrodynamic warnings
• Minimum wave frequency (rad/s) >
• Distance above sea bed must be > 0.5 rf
• Longest side < 1/7 wavelength
– Fatal error if more than %5 fail
• Nodes are not connected to another element = warning
dg /05.0
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...Aqwa-Line
Aqwa-Intro_14.5_WS03.1_Aqwa-Line.pptx
© 2012 ANSYS, Inc. May 8, 2013 35 Release 14.5
E. Aqwa-Librium
Introduction • Equilibrium position, Static and Dynamic (oscillatory) stability
• Complex ship/offshore structure systems;
• Various mooring, fender, pulley, winch, constraints configuration;
• Equilibrium estimation under wave, wind and current combination;
• Database approach for static catenary mooring line;
• Finite element approach for dynamic cable (drag force);
• Iteration approach for determining equilibrium position;
• Calculate the eigenvalues of linearized stiffness matrix to obtain static stability;
• Eigenvalues of the impedance matrix to give dynamic (oscillatory) stability.
• Series of wave spectrums
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...Aqwa-Librium Theory in Aqwa-Librium
• Equation for determining static equilibrium position
• K is the stiffness matrix of the system,
• F is the force matrix.
• The program iterates until X=|Xj+1-Xj| is less than a defined tolerance
• Static stability
• Eigenvalue λ (<0, unstable; =0, neutral; >0, stable)
• Dynamic stability
• Eigenvalue λ
• f<0, stable (converging oscillations);
• f>0 and g=0, unstable (steady oscillations);
• f>0 and g≠0, unstable (oscillatory divergence)
)()(1
1 jjjj XFXXX
K
0 XX K
),,0from(
,0
igfeXXXX
X
X
X
X
t
KCM
0I
KMCM11
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...Aqwa-Librium Analysis procedure
A common method of analysis
• run Stages 1 to 3 in Aqwa-Line
• run Stages 4 to 5 in another program, e.g. Aqwa-Librium
Aqwa-Line Run Stages 1 to 3
Aqwa-Librium Run Stages 4 to 5
Input Files Output Files Input Files Output Files
Tanker.dat Tanker.lis Tanker.res Libtank.lis
Tanker.hyd Libtank.dat Libtank.eqp
Tanker.plt Libtank.res
Tanker.res
Referenced in RESTART
command starting from
Column 21
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...Aqwa-Librium Analysis procedure
Stage 4 in Aqwa-Librium
• Model definition restart file
• Hydrodynamic database restart file
• Main analysis parameters input data file
Note
• Decks 1 to 8 data is read from the restart file
• Decks 9 to 20 are required in the input data file
• Decks 1 to 8 must be omitted
Stage 5 in Aqwa-Librium (Solution, no extra input)
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...Aqwa-Librium Alternative analysis
This approach allows for model changes directly within a mooring analysis
• run Stages 1 to 3 in Aqwa-Line
• run Stages 1 to 5 in another program, e.g. Aqwa-Librium
Aqwa-Line Run Stages 1 to 3
Aqwa-Librium Run Stages 1 to 5
Input Files Output Files Input Files Output Files
Tanker.dat Tanker.lis Tanker.hyd Libtank.lis
Tanker.hyd Libtank.dat Libtank.eqp
Tanker.plt Libtank.res
Tanker.res
Referenced in FILE
command in deck 6
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...Aqwa-Librium Analysis procedure
Stage 1-3 in Aqwa-Librium
• Model definition input data file
• Hydrodynamic database hyd file
• Main analysis parameters input data file
Stage 4 in Aqwa-Librium
• Main analysis parameters input data file
Note • Decks 1 to 20 data is read from the data file, but the
hydrodynamic database is not recomputed, it is copied from the previous Aqwa-Line run
• Decks 1 to 8 must be included
Stage 5 in Aqwa-Librium (Solution, no extra input)
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...Aqwa-Librium Data Requirements JOB TANK LIBR
TITLE SINGLE BOX WITH LINEAR MOORING
OPTIONS REST PBIS END
RESTART 4 5 Tanker
09 NONE
10 NONE
11 NONE
12 NONE
13 SPEC
13SPDN 315.0
END13PSMZ 0.3000 2.0000 4.000 8.000
14 MOOR
14LINE 1 5001 0 6001 1.50E6 99.5
14LINE 1 5002 0 6002 1.50E6 99.5
14LINE 1 5003 0 6003 1.50E6 99.5
14LINE 1 5004 0 6004 1.50E6 99.5
END14
15 STRT
15POS1 100.00 0.000 0.000 0.000 0.000 0.000
END
16 LMTS
END16MXNI 200
17 NONE
18 NONE
19 NONE
20 NONE
JOB card
Read database
Deck 9: drift motion parameters
Deck 10: wind and current drag
Deck 11: environment
Deck 12: constraints
Deck 13: spectrum
Deck 14: Mooring system
NB new nodes needed
Deck 15: Initial position of COG in global frame
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… Aqwa-Librium Options
Following Option cards can be used in Deck 0:
Option Function
STAT Static stability only (in JOB Card)
DYNA Dynamic stability only (in JOB Card)
PBIS Print Both Iteration Steps (prints full results at each step, in OPTION card)
PRAF Print all freedoms (in spite of DACF cards on DECK12, in OPTION card)
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… Drag in AQWA
Current and Wind Force Coefficients (Deck 10) DIRN Dir#1 Dir#n 1 …. n (optional)
SYMX (optional)
CUFX Dir#1 Dir#n C1 …. Cn
WIFX Dir#1 Dir#n C1 …. Cn
– Dir: direction number – directions default to Aqwa-Line wave directions;
– C: Drag Force Coefficients
• For relative current velocity V in direction
– force in X direction = CUFX.V2
– force in Y direction = CUFY.V2
– yaw moment = CURZ.V2
If DIRN is not present in Deck 10,
the default directions are those
defined on the DIRN cards in Deck 6
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... Drag in AQWA
Morison Drag Coefficients (for Ship Hull)
• Hull drag force on a diffracting structure to be calculated in a similar way to that for Morison element (velocity squared dependency)
MDIN Nrow Ncol C1 …. C6
– Nrow: Row number in drag matrix
– Ncol: Column number in drag matrix
– C1 – C6: Drag Force Coefficients
.
.
.
.
.
.
.
666564636261
565554535251
464544434241
363534333231
262524232221
161514131211
zz
yy
xx
CCCCCC
CCCCCC
CCCCCC
CCCCCC
CCCCCC
CCCCCC
DragForce
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… Static Environmental Conditions
Define current and wind conditions
Provides for slab (CURR) and profiled (CPRF) currents
CURR 0.75 120.0 CPRF -300.0 0.50 120.0
CPRF -150.0 0.70 120.0
CPRF 0.0 0.85 120.0
CURR velocity direction CPRF zpos velocity direction
Wrt FRA
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… Dynamic Environmental Loading
Regular (Naut only) or irregular wave information
Wind spectra
Constant current and wind (but only slab currents may be defined)
Cross swell spectrum
Note that Drift and Naut also permit import of pre-defined time histories of the following:
Wind speed and direction
External forces
Wave surface elevation
and also permits “on the fly” external force calculation through a dll interface
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… Dynamic Environmental Loading
Wave spectrum definition
• Jonswap
• JONH startfreq finfreq gamma Hs Fp
• Pierson Moskowitz
• PSMZ startfreq finfreq Hs T0
• User defined
• UDEF freq ordinate
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… Dynamic Environmental Loading
Wind spectrum definition
• Ochi and Shin wind spectrum
• OCIN
• API wind spectrum
• APIR
• NPD wind spectrum
• NPDW
• User defined
• UDWD cf cs I(z)
For wind spectrum the wind definition includes a reference height
• WIND velocity direction refHeight
• Note that if reference height is given, but no wind spectrum data is defined, AQWA will default to Ochi and Shin
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… Mooring Lines
Mooring Lines are defined in Deck 14 and can be used for Librium, Fer, Drift & Naut
• Linear Elastic Line (weightless)
LINE Ns1 Nd1 Ns2 Nd2 K L
Ns1, Ns2 structure numbers
Nd1, Nd2 node numbers
K stiffness
L unstretched length
• Polynomial Elastic Line (weightless)
POLY K1 K2 K3 K4 K5
NLIN Ns1 Nd1 Ns2 Nd2 (Ts) L (Fw) (Fp)
K1, .., K5 tension coefficients
Ts winch tension
Fw winch winding in friction factor
Fp winch paying out friction factor
Ts, Fw and Fp are only needed when the POLY line is used as a winch
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... Mooring Lines • Composite Elastic Catenary (with weight)
COMP Nz Nx Ne Zmin Zmax Slope
ECAT M1 A1 EA1 Tmax1 L1
ECAT M2 A2 EA2 Tmax2 L2
ECAT M3 A3 EA3 Tmax3 L3
NLIN Ns1 Nd1 Ns2 Nd2
Nz, Nx number of database points within z and x ranges (see next slide)
Ne number of ECAT in this COMP line.
Zmin/Zmax Z range (measured from the anchor) for the attachment node.
Slope sea bed slope (in degrees; positive for slope going up from anchor towards attachment point).
M1/2/3 mass per unit length for ECAT 1,2,3.
A1/2/3 equivalent cross section area.
EA1/2/3 Young’s modulus x area.
Tmax1/2/3 maximum tension.
L1/2/3 length of ECAT 1,2,3.
Ns/Nd structure and associated node numbers (Ns1: fairlead structure).
Start from anchor point
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... Mooring Lines Quasi-Static Mooring Line Database
ZRMAX
ZRMIN
XRMIN XRMAX
Max. tension point
Slack point
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… Other Mooring Data
Fenders 14POLY K1 K2 K3 K4 K5
14FEND Size Kf Kc
14FLIN Type Ns1 Nd1 Nd2 Ns2 Nd3 Nd4
K1 – K5 non-linear stiffness coefficients
Size uncompressed size of fender (normal direction)
Kf tangential friction coefficient
Kc normal damping coefficient
Type 1 = fixed fender, 2 = floating fender
Ns1 Structure to which fender is nominally attached
Nd1, Nd2 Nodes defining attachment point and contact plane on 1st structure
Ns2 Structure which fender contacts
Nd3, Nd4 Nodes defining contact plane on 2nd structure
Note: Be aware of valid range of force – extension/compression relationship
5)(5
4)(4
3)(3
2)(21
XKXKXKXKXKT
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... Other Mooring Data
Refer to AQWA Reference Manual for more details
CARD Definition
BUOY/CLMP A buoy or clump weight
TELM Tether element. (for installed or towed stiff tethers)
WNCH Constant tension winch line
FORC A constant force in a constant direction
LINE/PULY Linear elastic pulley line
LE2D User defined tension/extension data base
SWIR Steel wire with non-linear stiffness
DWT0/LNDW A line winding in or out on a winch
LBRK Line breaking
FILE Read in mooring definition from an external file *.MOR
With weight
(COMP/ECAT,NLIN,
NLID)
Without weight
(LINE,NLIN)
© 2012 ANSYS, Inc. May 8, 2013 54 Release 14.5
… Initial Conditions
Define starting vessel positions (and velocities) • Librium and Fer
POSn xpos ypos zpos rxpos rypos rzpos
• Naut
POSn xpos ypos zpos rxpos rypos rzpos
VELn xvel yvel zvel rxvel ryvel rzvel
• Drift
POSn xpos ypos zpos rxpos rypos rzpos
VELn xvel yvel zvel rxvel ryvel rzvel
SLPn xpos ypos zpos rxpos rypos rzpos
SLVn xvel yvel zvel rxvel ryvel rzvel
Can use RDEP option to automatically utilize results from a previous Aqwa-Librium run
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… Printing Options By default, not all results are output to limit file size
Additional data can be output by including specific commands
Can also be used to reduce the amount of data output
Command Definition
ALLM Output the velocity, acceleration and position of a user specified node defined in the NODE command
NODE Output the motion of a user specified node or the relative motion between two user specified nodes
PREV Write into *.LIS file every N time steps to reduce the size
PRNT Print a force not in the output by default (See Aqwa-ref 4.18.6)
PTEN Output mooring tension, anchor uplift, laid length etc for mooring line
ZRON Output the z position of a node relative to the incident wave surface
PMST Output mooring sectional tensions for cable dynamic case
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...Aqwa-Librium
Aqwa-Intro_14.5_WS03.2_Aqwa-Librium.pptx
© 2012 ANSYS, Inc. May 8, 2013 57 Release 14.5
F. Aqwa-Fer
Introduction
• Principally for calculating the significant response of amplitudes in irregular waves.
• Frequency domain program
• Linearized stiffness matrix / damping to obtain the transfer function and response spectrum
• Simple, inexpensive approach to make systematic parameter study
• Series of wave spectrums and mooring configurations
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...Aqwa-Fer
Typical applications:
• Calculation of wave frequency RAOs for uncoupled/coupled moored structures.
• Calculation of significant motions and tensions for the system due to wave frequency (high frequency) excitation.
• Calculation of significant motions and tensions for the system due to drift frequency (low frequency) excitation.
• Calculation of significant motions and tensions for the system due to wave frequency and drift frequency excitation combined.
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...Aqwa-Fer
Theory in Aqwa-Fer
• Response spectrum in irregular waves
Sxixi(ω): response spectrum in i-th degree of freedom,
Hij (ω) : receptance matrix defined as:
Fj(ω): frequency dependent force (in j-th degree of freedom) on the
structure
S(ω): the wave spectrum
)())]()(([mod)( 2 SFHS jij
j
xx ii
12 ])())(([)( CBiMMH asij
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...Aqwa-Fer
Linearization in Fer
• Stiffness: stiffness (hydrostatic, mooring etc. ) at the initial position
( = the static equilibrium position with RDEP option)
• Damping:
cable drag is linearized using the RMS velocity, when NLID used
FD = (CD. |VRMS|) .V
wind drag is linearized,
1st order hydrodynamic damping
any other input damping (fender, constraints)
• Forces: 1st and 2nd order wave forces
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Typical Force-Extension curve for catenary mooring
Extension Initial position
Force
Working range
Aqwa-Fer uses stiffness (i.e. slope) at initial position
Aqwa-Drift/Naut uses changing stiffness over working range
...Aqwa-Fer Linearization
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… Aqwa-Fer Options
Following Option cards can be used in Deck 0:
Option Function
DRFT Drift frequency only (in JOB Card)
WFRQ Wave frequency only (in JOB Card)
RDEP Read Equilibrium Position (in OPTION card)
FQTF Use full matrix of difference frequency QTF’s (in OPTION card)
PRRI Printing RAO’s at spectrum integration points (in OPTION card)
GLAM Output significant motions in GLOBAL axis (in OPTION card)
© 2012 ANSYS, Inc. May 8, 2013 63 Release 14.5
G. Aqwa-Drift & Naut
Introduction
• Aqwa-Naut and Drift are time-domain simulation programs
• For a series of time-steps they:
• calculate the total force on the structure
• calculate the acceleration
• find the new position of the structure
• A two stage predictor/corrector integration scheme is used
© 2012 ANSYS, Inc. May 8, 2013 64 Release 14.5
...Aqwa-Drift & Naut Equations of motion in time domain
• F(t) is the total force on the structure, including
• Incident wave force
• Diffraction force
• Drift force
• Mooring force
• Radiation force (damping)
• ...
• The equations of motion are solved in convolution integral form;
F(t)(t)XΜ..
s
)()()()()()]([ 1
0
tFdXttKXtX
t
as hMM
© 2012 ANSYS, Inc. May 8, 2013 65 Release 14.5
...Aqwa-Drift & Naut Simulation of irregular waves
• Wave spectra processing:
• Spectrum is split into sections of equal area for integration
• Wave components are defined with frequency at the centre of the section (Max. 200)
• Wave components are added together with random phase angles
iii
N
iiiiii Satykxkatyx
)(2),sincoscos(),,(1
ω
Wave component: equal areas
S(ω)
© 2012 ANSYS, Inc. May 8, 2013 66 Release 14.5
...Aqwa-Drift & Naut
Drift vs. Naut
Drift Naut
Irregular waves only Regular or Irregular waves
Linear hydrostatic stiffness (mean water surface)
Non-linear hydrostatics and incident wave forces (instantaneous wave surface)
2nd order drift forces 2nd order incident wave (omits drift forces but some 2nd order effects)
© 2012 ANSYS, Inc. May 8, 2013 67 Release 14.5
H. Summary
Linearity in Aqwa Programs
Hydro-
Statics
Diff /
Radiation
Froude-
Krylov
Drift
Force
Mooring
Force Drag
Line LIN LIN LIN 2nd order - -
Librium
eqm NON LIN LIN 2nd order NON Linearised
Librium
stability LIN LIN LIN 2nd order LIN Linearised
Fer LIN LIN LIN 2nd order LIN Linearised
Drift LIN LIN LIN 2nd order NON NON
Naut NON LIN NON - NON NON
© 2012 ANSYS, Inc. May 8, 2013 68 Release 14.5
… Aqwa-Drift Options
Following Option cards can be used in Deck 0:
Option Function
WFRQ Include wave frequency effects (in JOB Card). By default only drift effects are computed.
CONV Use Convolution (in OPTION card)
PBIS Print both integration steps (in OPTION card)
RDEP Read equilibrium position (in OPTION card)
FQTF Use full matrix of difference frequency QTF’s (CQTF OPTION in Line calculation is a prerequisite, in OPTION card)
© 2012 ANSYS, Inc. May 8, 2013 69 Release 14.5
… Aqwa-Naut Options
Following Option cards can be used in Deck 0:
Option Function
IRRE Irregular wave analysis (in JOB Card, CONV mandatory)
CONV Use Convolution (in OPTION card)
LSTF Linear stiffness. Uses hydrostatics from Line without modification (in OPTION card)
RDEP Read equilibrium position (in OPTION card)
© 2012 ANSYS, Inc. May 8, 2013 70 Release 14.5
… Time integration data for Drift and Naut
Provides time step and duration for a simulation
TIME number timestep start
number number of time steps
timestep time step interval
start optional start time (default is 0.0)
Aqwa also provides for restarting from a previous analysis - HOTS
© 2012 ANSYS, Inc. May 8, 2013 71 Release 14.5
...Aqwa-Fer
Aqwa-Intro_14.5_WS03.3_Aqwa-Fer.pptx
© 2012 ANSYS, Inc. May 8, 2013 72 Release 14.5
...Aqwa-Drift & Naut
Aqwa-Intro_14.5_WS03.4_Aqwa-Drift.pptx
Aqwa-Intro_14.5_WS03.5_Aqwa-Naut.pptx