HydroD Workshop Semisub1

Sesam – HydroD/Wadam workshop Global response analysis

Page 1 May13, 2012 © DNV Software. All rights reserved.

Sesam User Course – HydroD Wadam Workshop 1: Hydrodynamic analysis of a semi-submersible

This workshop is based on the following models created by GeniE: - Panel model – T1.FEM - Morison model – T2.FEM - Structural (FE) model & Mass Model – T3.FEM (Analysis 2 only) - The models are found on the given training course CD/memory stick or here:

C:\Program Files\DNVS\HydroD V4.5-08\Examples\SemisubWadam The model with its main dimensions is shown below. Note: All models will be translated -13 m in z direction The workshop may be performed from Brix Explorer of from HydroD directly


Start HydroD and create a new workspace You start HydroD from

- Start All Programs|DNV Software\Applications|HydroD V4.5-08

You create a new workspace (or a project) from File|New Workspace and give it a name

- For this workspace we use units meters and Newton - In this tutorial we have used the default installation directory which is

C:\DNV\Workspaces\HydroD. You may of course use other directories.

May13, 2012 © DNV Software. All rights reserved. Page 2



The use of a Wizard is recommended. When used, it will guide you through the different steps needed for the kind of analysis you select.

The Wadam wizard is started either from the Tools menu or from the toolbar

The options are - Panel Model only - Morison Model only - Composite Model – both a panel and a Morison model - Dual Model – a panel and a corresponding Morison model

In this workshop, you should select Composite Model

GUI of HydroD



The Wizard window may be made larger by normal window operations – Click and drag at the borders of the window.

There is a short description of some important features for each of the options When having selected Composite Model, the next operation is to click on the Settings tab.

Use of Wizard

In the Settings tab, select the features you want to include in the analysis

- This will set up the steps of the wizard, other features may be added later, if necessary

In this workshop, select the following features:

- Frequency domain - Element model - Stochastic drag - Offbody points



Direction set After clicking OK in the first wizard window, the wizard

will guide you through the steps Click the ‘First step’ button

and in the Create/Edit Direction dialog enter the values 0, 90 and 15 in the first three fields. When clicking ‘Fill table’ seven directions are filled into the table.

Click Apply followed by Cancel to proceed with the wizard.

You may also type the numbers in manually

Frequency set

Click the ‘Next step’ button. Select Period, enter the values 4, 38 and 2 and click

Fill table. Click Apply followed by Cancel to proceed with

the wizard.



Wave spectrum Create a Bretschneider spectrum with significant

wave height = 10 and peak period = 12. Click the eye

button to fit the graph in the area.

Click Apply followed by Cancel to proceed with the wizard.

The spectrum will be used in the linearization of drag

Spreading function Fill in exponent = 2 for the spreading function

(short crested sea). Click Apply followed

by Cancel to proceed with the wizard.



Wave spreading direction Create a direction = 45 which will be the main

direction of wave propagation. The spreading will be based on this direction.

Location The water depth is 300. Create a location with data

for water as shown below.



Frequency domain condition A frequency domain condition is created by

selecting a previously defined direction set and frequency set.

The wave amplitude option is valid for a Wasim analysis only, not for Wadam

Sea state Definition of the sea state to be used in the

drag linearization Give data as shown for the sea state:

- Sea state duration is 3 hours. Select spreading function and main heading by clicking the down-arrows next to the fields.

- Select a previously defined wave spectrum by clicking in the field and see that a down-arrow appears allowing the spectrum to be chosen. Notice the help text when positioning the mouse over the column header in the table.



Hydro model The hydro model is, as we will see later, an

assembly of models. Create a floating hydro model.

The bottom part of the dialogue is not used in context of Wadam (only Stability and Wasim, as explained from the information symbols)

Morison model Browse to find the Morison model T2.FEM. This model is typically created in GeniE



Morison section In this case the Morison elements will not

be part of a dual model. We will keep the diameter as defined on the T2.FEM file. The default values for the drag coefficients are kept.

When the Morison model is properly defined, it will be displayed

- This Morison model only covers the 2 braces



Pressure area Pressure Area elements are used to provide

longitudinal loads for the 2D Morison elements. In this case these elements are employed to ensure

correct loading of the interface between the panel model and Morison model.

Click Generate All Automatic (do not click OK): - The diameter will be taken from the Morison

element cross section, i.e. diameter = 2. After the translation of the model, the waterline

is at Z = 0.

Pressure area element If the previous pressure area section is created

automatically, this step can be skipped - Click Next

If not, enter waterline = 0 and click

Generate All Automatic.



Panel model Browse to find the panel model T1.FEM. The panel model is double-symmetric.

Loading conditions The Z-waterline is at z=13. It is also

possible to click Compute from mass to request the program to compute a waterline based balance of mass and displaced water.

Do not press Compute from mass this time


Mass model The mass model will be specified by first clicking

on Homogeneous Density Panel Model and then Fill from buoyancy

- Use the default distance of 3m between COB and COG - Replace all the very small numbers with 0 - Notice the different coordinate systems and the information from the light bulb. - The “COG Centered Coordinate System” is the default option


21



Offbody points Offbody points may be used to either,

- define points at which to calculate wave pressures and wave particle velocities in Wadam. These results can later be post-processed in Postresp, or

- define a grid to represent the sea surface which can later be animated together with vessel RAOs in Xtract.

We will use the first option in Analysis 1 and the second option in Analysis 2

Offbody points (Analysis 1) Select ‘Specified’ and enter three points

in the Table, i.e.

- 0. 0. 0 - 27 0 0 - 0 27 0

- Z = 0 means the points are defined

in the free surface

These points will be used in further computations of air gap etc. in Postresp



Create Run Fill in the various tabs as shown. Otherwise

accept default data.



Create Run, continued



Analysis Clicking the Last step button of the wizard opens

the dialog for running Wadam. Or, run the Wadam analysis by selecting WadamRun1in the dialog below to the right

Run the Wadam analysis by starting WadamRun1 in the Activity Monitor. View print file as shown below. If you have closed the dialog reopen it as shown to the right.

The print-out from Wadam should be checked with respect to, among other things, any warnings or errors and model properties such as mass and buoyancy data and motion characteristics.

The bottom line should read: P R O G R A M N O R M A L E N D

The result files are located in the WadamRun1 directory in the current workspace - Important files

- wadam1.lis - G1.sif

After a successful Wadam run, the next typical steps are to use the postprocessors Postresp – for statistical results – and Xtract – for animation of motions



Exit HydroD

Exit HydroD by using the Exit button in the upper right corner. Remember to save the database.

Save “Clean JS file” Use “File – Save Clean JS” to create a good backup

file for the model. This is a good habit when leaving a workspace. Even if all commands are saved in a sequential JS file, which may also be used as an input file, the “Clean” JS file is a lot better for backup etc. This file may be used to recreate the current workspace, without remembering the history, such as deleted and changed items etc.

The Save Report function could be tested as well - Select the HTML type, then click the

View button to see it

Documents

HydroD Workshop Semisub1