hydrod workshop semisub2

Sesam – HydroD/Wadam workshop Load transfer analysis

March 1, 2012 © DNV Software. All rights reserved.

Sesam User Course – HydroD Wadam Workshop 2: Hydrodynamic load transfer analysis of a semisubmersible

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



In this workshop we will use a new Wadam wizard Start HydroD and re-open the previous workspace (may done from Brix Explorer for Sesam). Start the Wadam wizard by clicking the button: Start by selecting the Composite Model and read the information provided in the Information

tab as shown below.

Then go to the Settings tab and enter data as shown to the right.

Click OK to proceed with the wizard.

Note that the first 8 steps for the environment may be skipped (to re-use the data from the first run).



Direction set 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.

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.

May be skipped



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.

Spreading function Fill in exponent = 2 for the spreading function

(short crested sea). Click Apply followed

by Cancel to proceed with the wizard.

May be skipped



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.

May be skipped



Frequency domain condition A frequency domain condition is created by

selecting a previously defined direction set and frequency set.

The wave amplitude is not used for a Wadam analysis

Sea state 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.

May be skipped



Hydro model 2 The hydro model is, as we will see later, an

assembly of models. Create a floating hydro model.

Morison model Browse to find the Morison model T2.FEM.

Morison section Use name like PIPE1a 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.



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: - The diameter will be taken from the Morison

element cross section, i.e. diameter = 2.

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.

Cross sections Define some cross sections where sectional loads

will be computed. - For example YZ, XZ and XY plane



Structure (FE) model Browse to find the structure (FE) model T3.FEM.

General Compartment properties Permeability The permeability of a compartment is a measure on

how much of the compartment/tank may be filled with liquid

- Permeability = 1

Deck tank property is used for stability analysis only - Select Next



Create Compartment This menu assigns the permeability

properties to the compartments In this case we use the same

permeability for all compartments

Note that you may change the view and change the display from the browser while the wizard is running

Loading conditions The Z-waterline is at 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



Compartment properties Fluid property The density of fluid in compartments is defined for

each loading condition

In this case we use the same density for all compartments = 900 kg/m3

The compartments are displayed in the structural model

Flooded compartment This definition is used to mark compartments

as flooded or not



Compartment properties Filling fraction The filling fraction of the compartments is defined for

each loading condition

In this case we use the same filling fraction of 1.0 for all compartments

Compartment content Properties of fluid (density), flooding and filling

fraction are assigned to the compartments The ‘Fill below’ button can be use to fill the same

property for all compartments



Mass model The mass model will this time be created by using the

Mass Model T3.FEM (same as the structural model)

Compartment balancing is not used, because we have the same fluid and filling ration in all compartments, click Next.

Offbody points Offbody points may be used to either,

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

- to define a grid to represent the sea surface which can then 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 2)

Select Points Grid and see the following grid to represent the sea surface

The points from this grid will be used in display and animations etc. in Xtract

Run Fill in the various tabs as shown. Otherwise

accept default data.



Run, continued

Add tolerances for load transfer

Keep drag as before



Run, continued

Include the static load, if wanted Specify first load case as 1 NOTE: Composite model load transfer can be done in two different ways, by using a

superelement structural model (several superelements) or by using a single superelement model

- When using the (several) superelement option, the Morison model should be included in the structural model as a separate superelement, meaning the structural model needs to be a superelement model consisting of a shell part and a beam (bracings) part, in two different T#.fem files coupled together at a top level. This workshop has a separate Morison superelement, but this is not included in the structural model. Consequently, the Morison loads will not be included in the structural analysis.

- When using the single superelement composite model, the complete structural model, including bracings etc., should be used also as the Morison model in HydroD. This is not the case in this workshop, but it may be achieved by replacing T2.FEM by T3.FEM and define the correct Morison sections.

Yes/No to Static load



Analysis Clicking the Last step button of the wizard opens

the dialog for running Wadam. Or, run the Wadam analysis by selecting WadamRun2in the dialog below to the right

Deselect WadamRun1. Start WadamRun2. See print file as shown below to the right. 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 - L*.fem (* = superelement number)

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



It is useful to verify the model and wave loads prior to the structural analysis

To start Xtract just right-click the WadamRun2 folder and select Xtract.

In Xtract, Double-click Toplevel in the Database view to view the model

- The model file T3.FEM, including the load file L3.FEM, and the Wadam result file, G1.sif, will be opened automatically

- Double-click Toplevel in the Database view to view the model

Some typical commands are: - Go to Resultcases at the bottom of the Database

view, select e.g. no. 5 - Double-click Elements – Surface loads – Normal pressure - Use ‘Display – Part Attributes’ to set the sea surface

transparent, remove contours and add mesh - Select ‘Model – Deformed’ and set ‘Model – Deformation Scaling’ to 5 (e.g.) - Go to ‘Animation – Frequency animation’. Use defaults. - Start the animation by selecting the ‘Play’ button - Zoom into the model - Rotate the model by with the right mouse button - Other buttons to frame the model and select views

If time allows, you should try out more features of Xtract

Run Xtract from HydroD



From the HydroD version 4.2-04, Sestra may be started directly from within HydroD - To run Sestra, just right-click the WadamRun2 folder and select Sestra - Sestra will automatically read the load file, L3.fem, and the S3.fem file.

Run Sestra from HydroD

This run of Sestra will produce the following files: - SESTRA.LIS Print-out from Sestra - FOR007 Additional file from Sestra, used primarily when an error is found

Otherwise called SESTRA.MNT - R3.SIN Results file

The print-out (SESTRA.LIS ) should be checked, especially with respect to sum of loads and

masses and reaction forces. The results file, R3.SIN, may be read into Xtract for further postprocessing.

hydrod workshop semisub2

Documents