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vk.com/club152685050Applying Ocean Loading from| vka Hydrodynamic.com/id446425943Analysis

The .ahd file contains data indicating which side of a panel is the wetted side. The program uses the data to adjust which direction to apply the hydrodynamic pressure on the SURF154 elements.

Each structural integration point is located in its nearest hydrodynamic panel. The program then calculates the corner pressures of the panel based on a weighted averaging of that panel and its neighboring panels. Finally, using a bilinear fit across the panel, the program calculates the hydrodynamic pressure

at the structural integration point.

18.2. Hydrodynamic Load Transfer with Forward Speed

Ocean loading analysis does not allow input of forward speed explicitly. To account for forward speed, it is necessary to specify an opposite current. If forward speed and a current are required, the specified current must represent the resultant of the two effects. This current is used only for the calculation of Morison loads following the diffraction calculation.

If the panel pressures and motions are obtained from AQWA, it is also possible to define a forward speed in the diffraction calculation, causing the hydrodynamic coefficients to be corrected for the effect of forward speed. The following restrictions apply:

Forward speed can be along the global X axis only.

Only one wave direction can be specified in a diffraction calculation with forward speed.

It is your responsibility to ensure that forward speed in the diffraction calculation and current in the load transfer are consistent.

18.3. Hydrodynamic Data File Format

The hydrodynamic data file comprises a number of sections which represent all of the required input to the ocean wave command:

18.3.1.Comment (Optional)

18.3.2.General Model Data

18.3.3.Hydrodynamic Surface Geometry

18.3.4.Wave Periods

18.3.5.Wave Directions

18.3.6.Panel Pressures

18.3.7.Morison Element Hydrodynamic Definition

18.3.8.Morison Element Wave Kinematics Definition

18.3.9.RAO Definition

18.3.10.Mass Properties

18.3.1. Comment (Optional)

The comment section contains descriptive text for the model.

* text

where

*keyword to signify that this is a comment line

text description of the model

 

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Hydrodynamic Data File Format

18.3.2. General Model Data

This section defines some general data for the model.

GENE

depth density gravity symxy

where

 

GENE

keyword to denote the start of the general model data

depth

water depth

density

water density

gravity

acceleration of gravity

symxy

symmetry integer

 

0: no symmetry

 

1: symmetry about x axis

 

2: symmetry about y axis

 

3:symmetry about both x and y axes

Example 18.1: General Model Data

GENE

 

 

 

2.500000E+02

1.025000E+03

9.800000E+00

3

18.3.3. Hydrodynamic Surface Geometry

The hydrodynamic surface geometry provides information related to the panel definition of the model. Allowance can be made for symmetric models; that is, only one half of the model must be defined for one plane of symmetry, and only a quarter of the model must be defined for double symmetry.

HYDR npan

x1(1) y1(1) z1(1) x2(1) y2(1) z2(1) x3(1) y3(1) z3(1) x4(1) y4(1) z4(1)

.

.

x1(npan) y1(npan) z1(npan) x2(1) … x4(npan) y4(npan) z4(npan)

where

 

HYDR

keyword to denote start of hydrodynamic panel description

npan

number of panels to be defined

xk(j)

X coordinate for panel j, node k

yk(j)

Y coordinate for panel j, node k

zk(j)

Z coordinate for panel j, node k

The nodes must be arranged in counterclockwise order when viewing the panel from the wetted side. To define a triangular panel, specify the same coordinates for nodes 3 and 4.

Example 18.2: Hydrodynamic Surface Geometry

HYDR 12

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18.3.4. Wave Periods

This section defines the wave periods where hydrodynamic pressures have been computed.

PERD nperd

period(1) period(2) ... period(i) period(i+1) period(i+2) ... period(nperd)

where

 

PERD

keyword to denote start of wave period data

nperd

number of wave periods

period(i)

the ith wave period (s)

The data may be specified in one or more lines until all the periods are entered.

Example 18.3: Wave Periods

perd 1 18.0

18.3.5. Wave Directions

This section defines the wave directions where hydrodynamic pressures have been computed.

DIRN ndirn

heading(1) heading(2) ... heading(i) heading(i+1) heading(i+2) ... heading(ndirn)

where

 

DIRN

keyword to denote start of wave direction data

ndirn

number of wave directions

heading(i)

the ith wave direction (in degrees, between -180 and +180)

The data may be specified in one or more lines until all the directions are entered.

Example 18.4: Wave Directions

dirn 2

0.090.0

 

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Hydrodynamic Data File Format

18.3.6. Panel Pressures

This section defines the wave directions where hydrodynamic pressures have been computed.

PRES

iperiod iheading region panel magnitude phase

where

PRES

keyword to denote the start of hydrodynamic pressure values

iperiod period number (position in the period list)

iheading wave direction number (position in the direction list)

region • If two planes of symmetry (symxy set to 3)

region 1 corresponds to modelled elements

region 2 corresponds to reflection in x-z plane

region 3 corresponds to reflection in y-z plane

region 4 corresponds to reflection in x-z and y-z plans

If one plane of symmetry (symxy set to 1 or 2) region 1 corresponds to modelled elements region 2 corresponds to reflected elements

panel panel number (must be between 1 and npan)

mag- pressure amplitude nitude

phase associated phase angle in degrees (with respect to the wave at the center of gravity of the vessel)

The associated phase angle (phase) determines the horizontal location of the loading. The magnitude and phase together define the shape of the harmonic loading curve.

Pressure is positive when acting from the wetted surface towards the inner surface.

If no input pressure is given to a panel at a particular period and direction, the pressure on the panel is assumed to be zero. If more than one set of pressures are defined, their effects are accumulative; that is, the real and imaginary parts of each set are summed together.

Example 18.5: Panel Pressures

PRES

 

 

 

 

 

1

1

1

1

25.0

0.0

1

1

1

2

75.0

0.0

1

1

1

3

100.0

0.0

1

1

1

4

100.0

0.0

1

1

1

5

25.0

0.0

1

1

1

6

75.0

0.0

18.3.7. Morison Element Hydrodynamic Definition

The data in this section describes the line elements used to provide slender body loading.

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