Lecture 03 14.5 Release
ANSYS Aqwa Suite
A. Core Aqwa Programs Aqwa-Line 3-D diffraction & radiation analysis program for wave force and structure structure response response calculations; 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 •
A. Core Aqwa Programs Aqwa-Line 3-D diffraction & radiation analysis program for wave force and structure structure response response calculations; 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 •
... 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; processor; on-line analysis analysis •
…Core Aqwa Programs ANSYS Mechanical
AGS
Line
Librium
Fer
Naut
Drift
EXCEL
B. AGS AQWA Graphical Interface can be used to; •
Generate Mesh (for ship shape models)
AQWA Graphical Supervisor AQWA Graphical Interface can be used to; •
Post process
•
Force & Response Curves
•
Shear Force & Bending Moment
AQWA Graphical Supervisor AQWA Graphical Interface can be used to; •
Post process – Pressure Contours – Wave Surface Contours – Diffracted Wave Surface
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
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
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.
AGS Analysis • Allows analyses to be run interactively.
AGS Graphs Allows graphical plotting of frequency and time domain information
AGS Model Visualization Provides geometry and results presentation
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
AGS Model Visualization View angle provides rotation of model view Rotations about screen Z axis Rotations about screen X axis
Isometric view
Elevations along X, Y, Z axes Direction of view controlled by + or – radio button
Current View Angle Angle increment C 30 degrees M 10 degrees F 1 degree
AGS Model Visualization Zoom buttons provide zoom in/out facilities Size to screen Zoom in +/out -
Current View Size
Zoom increment C Coarse F Fine
Can also zoom in/out by left mouse button “rubber band” on image
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
Only one of these boxes will be selected at any time. They indicate which structure the position information relates to
These boxes determine which structures are visible. Red indicates visible, white is not visible. Click on box to change status
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
AGS Cable Dynamics Allows for additional processing and visualization of mooring line cable dynamics
C. AQWA Suite need to knows
File names
File types Deck system Restart stages
...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!
...AQWA Suite need to knows Input/Output Files • • • • • • • • • • • • • • • • • •
*.dat *.lin *.sfm *.wht *.wvt *.xft *.mor *.res *.hyd *.eqp *.uss *.pot *.mes *.lis *.pos *.plt *.pac *.vac
input data file (ASCII, LBDNF) input file for AGS mesh generator (ASCII) input mass distribution for splitting forces (ASCII, AGS) a wave height time history (ASCII, D) a wind velocity time history, no card needed (ASCII, DN) an external force time history, no card needed (ASCII, DN) mooring description file (ASCII, BDNF) restart file (binary, LBDNF) hydrodynamics file (binary, L) equilibrium position file (binary, B) source strength file (binary, L) potential file (binary, L) output message file (ASCII, LBDNF) output listing file (ASCII, LBDNF) output position file (binary, DN) output graphic file (binary, LBDNF) pressures at centroids (binary, L) velocities at centroids (binary, L)
See Aqwa-Ref 1.3 for details
...AQWA Suite need to knows Input data (*.dat) file •
•
•
ASCII text file containing all the input data necessary for the Stages Stages of of Analysis about to be executed. in FIXED FORMAT and must be entered using a text editor. 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 PLANS/SCA LING OPTIONS REST END RESTART 1 2 4col 4col5cols5cols 10 cols 10 cols 10 cols 01 COOR 01 1 END01 999
45.000 0.000 Column 21
02 ELM1 02QPPL DIFF
0(1)(
06FREQ
6
1
1)(
0.10472
-45.000 0.000
2)( 0.15708
0.000 -10.620
12)(
11)
0.25133
0.41888
0.52360
...AQWA Suite need to knows Restart File (.res) This is a binary file, 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
...AQWA Suite need to knows Hydrodynamic File (.hyd) •
This is a binary file, 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)
Comparison of Comparison of .RES and .HYD (after Aqwa-Line solution solution)) 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
...AQWA Suite need to knows Graphical Plot File (.plt) 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
...AQWA Suite need to knows Deck # 0
Overall administration parameters
1
Node coordinates
2
Element definitions
AQWA Data (.dat) file has a predetermined deck system
3
Material properties
4
Geometric properties
Each deck begins with a header, and terminates with an END statement, with the associated data defined between these statements
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
Deck system (now referred to as Data Category) •
•
Deck header 01 COOR 01 1 01 999
45.000 0.000
-45.000 0.000
0.000 -10.620
END
Deck terminator •
Description
Further explained later and in Workshops!!
Data
19/20
Reserved for future use
21
Element and nodal loads
...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 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)*
-
* Calculation Stage Only
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)
...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
...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
...Aqwa-Line Geometric Property Warnings •
Area ratio of adjacent elements < 3
•
Aspect ratio (AR) > 1/3, where
AR
(C = 1 for quadrilateral elements,
area 2
l ongest si de
.C
C = 2.3 for triangular elements) •
Element centres must be at least one facet radius (r f ) apart,
•
Shape factor (parameter for regularity of panel)
•
<0.2 = warning
•
<0.02 = fatal error
•
See AQWA Theory Manual for more detail
r f
area
...Aqwa-Line Hydrodynamic warnings •
Minimum wave frequency (rad/s) >
•
Distance above sea bed must be > 0.5 r f
•
Longest side < 1/7 wavelength
0.05
g / d
– Fatal error if more than %5 fail
•
Nodes are not connected to another element = warning
...Aqwa-Line Aqwa-Intro_14.5_WS03.1_Aqwa-Line.pptx
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
...Aqwa-Librium Theory in Aqwa-Librium •
Equation for determining static equilibrium position X j
•
X j
1
K
( X j ) F ( X j )
•
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 •
•
1
K X
X
0
Eigenvalue λ (<0, unstable; =0, neutral; >0, stable)
Dynamic stability
M 1C I
M
1K X 0
X 0, X X
C X K X 0, X e t , (from M X
•
Eigenvalue λ
•
f<0, stable (converging oscillations);
•
f>0 and g=0, unstable (steady oscillations);
•
f>0 and g≠0, unstable (oscillatory divergence)
f ig )
...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
...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)
...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
...Aqwa-Librium Analysis procedure Stage 1-3 in Aqwa-Librium Model definition Hydrodynamic database Main analysis parameters
input data file hyd file 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)
...Aqwa-Librium Data Requirements JOB card
JOB TANK LIBR TITLE
SINGLE BOX WITH LINEAR MOORING
OPTIONS REST PBIS END RESTART 4 5 09
NONE
10
NONE
11
NONE
12
NONE
13
SPEC
Tanker
13SPDN
Deck 9: drift motion parameters Deck 10: wind and current drag Deck 11: environment Deck 12: constraints Deck 13: spectrum
315.0
END13PSMZ 14
Read database
0.3000
2.0000
4.000
8.000
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
Deck 14: Mooring system NB new nodes needed
END14 15
STRT
15POS1
100.00
0.000
0.000
0.000
0.000
0.000
END 16
LMTS
END16MXNI 17
NONE
18
NONE
19
NONE
20
NONE
200
Deck 15: Initial position of COG in global frame
… 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)
… Drag in AQWA Current and Wind Force Coefficients (Deck 10) DIRN
Dir#1
Dir#n
1 ….
n
SYMX
(optional) (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
... 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
C 11 C 21 C 31 DragForce C 41 C 51 C 61
C 12
C 13
C 14
C 15
C 16 x. x
C 22
C 23
C 24
C 25
C 32
C 33
C 34
C 35
C 26 y . y . z C 36 z
C 42
C 43
C 44
C 45
C 52
C 53
C 54
C 55
C 62
C 63
C 64
C 65
. . C 46 . C 56 . C 66
… Static Environmental Conditions Define current and wind conditions Provides for slab (CURR) and profiled (CPRF) currents
Wrt FRA CURR velocity direction CURR 0.75 120.0
CPRF zpos velocity direction CPRF -300.0 0.50 120.0 CPRF -150.0 0.70 120.0 CPRF 0.0 0.85 120.0
… 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
… 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
… Dynamic Environmental Loading Wind spectrum definition •
Ochi and Shin wind spectrum •
•
API wind spectrum •
•
APIR
NPD wind spectrum •
•
OCIN
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
… 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
Ns1, Ns2
structure numbers
Nd2
K
L
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)
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
(Fp)
... Mooring Lines •
Composite Elastic Catenary (with weight) COMP
Ne
Zmin
Zmax
Slope
ECAT
M1
A1
EA1
Tmax1
L1
ECAT
M2
A2
EA2
Tmax2
L2
ECAT
M3
A3
EA3
Tmax3
L3
Ns2
Nd2
NLIN
Nz
Ns1
Nx
Nd1
Start from anchor point 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).
... Mooring Lines Quasi-Static Mooring Line Database XRMIN
XRMAX
ZRMAX
ZRMIN
Max. tension point
Slack point
… Other Mooring Data Fenders 14POLY
K1
K2
K3
K4
K5
14FEND
Size
Kf
Kc
14FLIN Type
Ns1
Nd1
Nd2
Ns2
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
Nd3
Nd4
Note: Be aware of valid range of force – extension/compression relationship T K X K
1
2
( X )
2
K
3
( X )
3 K X 4 ( ) 4
K
5
(X )
5
... 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)
… Initial Conditions Define starting vessel positions (and velocities) •
•
•
Librium and Fer POSn
xpos
ypos
zpos
rxpos
rypos
rzpos
POSn
xpos
ypos
zpos
rxpos
rypos
rzpos
VELn
xvel
yvel
zvel
rxvel
ryvel
rzvel
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
Naut
Drift
Can use RDEP option to automatically utilize results from a previous Aqwa-Librium run
… 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
...Aqwa-Librium Aqwa-Intro_14.5_WS03.2_Aqwa-Librium.pptx
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
...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.
...Aqwa-Fer Theory in Aqwa-Fer •
Response spectrum in irregular waves S xi xi ( ) [mod ( H ij ( ) F j ( ))]2 S ( ) j
Sxixi(ω):
response spectrum in i-th degree of freedom,
Hij (ω) :
receptance matrix defined as: H ij ( ) [ 2 ( M s
F j(ω):
frequency dependent force (in j-th degree of freedom) on the structure
S(ω):
1
M a ( )) i B( ) C ]
the wave spectrum
...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
...Aqwa-Fer Linearization Typical Force-Extension curve for catenary mooring
Force
Working range
Initial position
Extension
Aqwa-Fer uses stiffness (i.e. slope) at initial position Aqwa-Drift/Naut uses changing stiffness over working range
… 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)
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
...Aqwa-Drift & Naut Equations of motion in time domain ..
Μ s
•
•
X (t)
F(t)
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; t
(t ) KX (t ) [M s M a ()] X
h(t 0
( )d F (t ) ) X 1
...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 N
( x, y, t ) ai cos(k i x cos k i y sin it i ), ai 2S ( i ) i i 1
S(ω) Wave component: equal areas
ω
...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 2 nd order effects)
H. Summary Linearity in Aqwa Programs Hydro-
Diff /
Froude-
Drift
Mooring
Statics
Radiation
Krylov
Force
Force
LIN
LIN
LIN
2 nd order
-
-
NON
LIN
LIN
2nd order
NON
Linearised
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
Line Librium eqm Librium stability
Drag
… 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)
… 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)
… Time integration data for Drift and Naut Provides time step and duration for a simulation
TIME
number
timestep
number
number of time steps
timestep
time step interval
start
optional start time (default is 0.0)
start
Aqwa also provides for restarting from a previous analysis - HOTS
...Aqwa-Fer Aqwa-Intro_14.5_WS03.3_Aqwa-Fer.pptx
