HydroD Semisubmersible Stability

DET NORSKEVERITAS1

SESAM - HydroD Stability and Hydrostatic Analysis

DNV Software – HydroD SemiSubmersible StabilityPrepared by Ole Jan NekstadRevised 21 May 2007

of SemiSubmersible

SESAM User Course in Stability and Hydrostatic AnalysisHydroD Workshop:

Perform the analysis in HydroD

• The text in this workshop describes the necessary steps to do stability and hydrostatic analysis of a semi-submersible as well as checking the compliance to hydrostatic rule checks IMO and NMD.

• The semi-submersible has 22 compartments which can be filled independently – in this workshop you are asked to do various tank fillings to see the effect on stability parameters like e.g. equilibrium position and the computed GZ-curves. Furthermore, the various tank fillings are used to define intact and damaged conditions necessary to perform the hydrostatic rule checks

• The panel model, structure model (used to describe the tanks) and the mass model have been created in GeniE. The total mass of the structure (mass model) is 21258990.81 Kg. The file describing the panel model is called Panel_T543.FEM (notice that this file uses a Panel_T1.FEM file), the structure model and the mass model is named Structure_T4.FEM.

• The max and min x-values are -40.3m and 40.3m

• In addition to the text input, there is also a journal file Semi_Submersible_Stability_in.jsthat you can read into HydroD to rapidly reproduce the workshop. Please make sure that the journal file and the FEM files have been copied to the project directory set up by HydroD. Alternatively, you may refer to all the files from the example directory.

• This workshop should be viewed on-line or on colour print out to best see the property colour coding.

Part 0 - General

Xmin = -40.3m Xmax = 40.3m

The model created in GeniE

DET NORSKEVERITAS2



of SemiSubmersible

Important notes:• The semi-submersible has 22 compartments as

shown. The compartments have been made using GeniE’s automatic features for compartment generation – of these 22 has been filled with liquid content to define which ones are subjected to hydrostatic analyses. The tank filling is done in HydroD by the user (or from using the feature for tank balancing).

• The wetted surface to describe the panel model has also been defined in GeniE.

• All compartment names have been automatically created based on modelling in Genie – you may change them in HydroD

• The structures are fictitious model

• The units are meter and kg.

• All pictures created by GeniE and HydroD are shown using white background (View|Options|General|PaperBackground). This may be different from your background.

Part 0 - General

The compartments as defined in GeniE, and an example of filling a

compartment with liquid

Model origin at (0m, 0m, 0m) as shown to the right

In total 22 compartments are imported to HydroD

DET NORSKEVERITAS3



of SemiSubmersiblePart 0 - General

The compartments Cm_LC2 to Cm_LC9 are located in the pontoon

corners

The compartments Cm_LC10 to Cm_LC17 are located in the deck

zone

The compartments Cm_LC18 to Cm_LC21 are located in the

pontoon centre

The compartments Cm_LC22 to Cm_LC23 are located in columns

DET NORSKEVERITAS4



of SemiSubmersible

The workshop is split as follows (start modelling from Part 1 and onwards)• Part 0 – General introduction to the workshop and start HydroD

Pages 1-5

• Part 1 – Using the stability wizard to make model and do initial analysisThe wizards will guide you through all necessary steps to make a model fit for stability and hydrostatic computations. This is useful also for experienced users, but similar modelling and analysis may be done by using pull-down menus, tool-buttons or from the context sensitive menu in the browser. Notice that all data that are created may be modified from the browser. Pages 6-34

• Part 2 – Modify cross sections and re-runMake new cross sections and re-run to display still water forces and momentsPages 35-39

• Part 3 – Make several loading conditions and execute simultaneouslyIn many cases it is necessary to define several floating conditions, e.g. special tank fillings or damaged conditions. This part shows how easy it is to create several conditions and how to run themPages 39 – 48

• Part 4 – Perform hydrostatic rule checksCheck the structure and loading conditions for compliance with NMD and IMO ModuPages 49 – 51

• Part 5 – Perform allowable vertical center of gravity analysisPerform allowable vertical center of gravity analysis according to NMD and IMO MODU rule setsPages 52 – 56

• Part 6 – Make a clean journal fileSave the input files (journal files) for later usePage 57

Part 0 - General

DET NORSKEVERITAS5



of SemiSubmersible

Start HydroD and make a new workspace• You start HydroD from

� Desktop

� Start All Programs|DNV Software\Applications|HydroD

• You make 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.

Part 0 - General

DET NORSKEVERITAS6



of SemiSubmersible

Activate the wizard• You activate the wizard from the tool-button

• You need to specify what type of model you will be working with, this workshop assumes a pure panel model

• You may also change the default settings (i.e. filter out steps in the wizards) by clicking on “Settings”

Part 1 – The stability wizard

DET NORSKEVERITAS7



of SemiSubmersible

Step 1 in the wizard• Create a location

• Specify name (“GoM” in this case), water density, kinematic viscosity and water depth

Step 2 in the wizard• Create a hydro model

• Specify a name and decide fixed or floating structure


DET NORSKEVERITAS8



of SemiSubmersible

Step 3 in the wizard• Create a panel model

• The panel model specifies the outer wetted surface. The wetted surface is being used to calculate the floater buoyancy.

� The panel model has been made in GeniE

� To import, locate the file Panel_T543.FEM stored under C:\Program Files\DNVS\HydroD\Examples\Semi. The path name assumes you have installed the program HydroD using default values when installingRemember that this file refers to Panel_T1.FEM

� There are no symmetry planes in this model and the coordinate system of the imported model coincides with the wanted coordinate system of the hydro model


DET NORSKEVERITAS9



of SemiSubmersible

Step 3 in the wizardCont’d

• The panel model is now shown in your display window

� Notice, the colours have been changed from default using the Modelling Draw Style Option. See an example of this later in this tutorial


DET NORSKEVERITAS10



of SemiSubmersible

Step 4 in the wizard• Create load cross sections

• One load cross section will be made using the wizard. Multiple cross-sections will be generated manually later in this tutorial

� The purpose of a load cross section is to define where HydroD shall compute still water forces and bending moments during hydrostatic analysis


DET NORSKEVERITAS11



of SemiSubmersible

Step 5 in the wizard• Create the structure

model. The tank definitions are now imported

• Similar to the panel model, the structure model has been created in GeniE.

� To import, locate the file Structure_T4.FEM stored under C:\Program Files\DNV`S\HydroD\Examples\Semi (remember that this file uses the Panel_T1.FEM file)

• The panel model and the structure model is now being shown in the graphical window


DET NORSKEVERITAS12



of SemiSubmersible


• Hint: You may switch your focus view by using the “Modelling Draw Style” feature

� Below is shown how to look at the structure model only and also how to change colours of the beams to dark blue

� Remove the panel modelfrom view


DET NORSKEVERITAS13



of SemiSubmersible


• Hint: You may switch your focus view by using the “Modelling Draw Style” feature

� The beams are now shown with dark blue colour.


DET NORSKEVERITAS14



of SemiSubmersible

Step 6 in the wizard• Define permeability factors

• Permeability factors are used to define whether a compartment can be filled entirely or not. Compartments may include internal parts like pumps etc. that are not modelled.

� For a permeability factor 1.0 there are no internal parts of the compartment, i.e. the entire volume may be filled

� For a permeability factor of e.g. 0.7, 70% of the compartments volume may be filled

• Define two permeability factors as follows

• You may edit the factors (or add new ones) from the browser area


DET NORSKEVERITAS15



of SemiSubmersible

Step 7 in the wizard• Define deck tank properties

• Deck tank properties are used to define whether a tank (compartment) is treated as a deck tank or not in connection with stability rule checking

� When deck tank properties are employed, two GZ-curves will be computed, one with the deck tanks intact and one with the deck tanks flooded.

• Define a deck tank property as shown to the right

Step 8 in the wizard• Define all the compartments

� Permeability of compartments (i.e. how much volume may be filled)

� Deck tanks for compartments 10-17


DET NORSKEVERITAS16



of SemiSubmersible

Step 9 in the wizard• Create a loading condition

• The first loading condition has a given draft and trim/heel as specified

• You should now also see the waterline


DET NORSKEVERITAS17



of SemiSubmersible

Step 10 in the wizard• Create fluid properties

• Fluid properties are used when filling the compartments. The compartments are filled according to these properties together with a filling fraction.

• Two properties are used in this tutorial: Oil and Seawater:

• You may edit the fluid properties from the browser


DET NORSKEVERITAS18



of SemiSubmersible

Step 11 in the wizard• Create flooded properties

• Flooded properties are used to specify whether a compartment is flooded or not.

� When a tank is flooded, the top level of internal fluid is always in line with the elevation of the sea surface.

� When the compartment is 100% below sea surface the tank is filled

Step 12 in the wizard• Create filling fractions

• Filling fractions are used to specify how much a compartment is filled.

� The filling degree may vary from 0 – 1

� Define 8 filling fractions as follows (they may be modified from the browser):


DET NORSKEVERITAS19



of SemiSubmersible

Step 13 in the wizard• Define the content of compartments

• The compartment content is now defined to consist of “intact fluid”, “damage fluid”, flooded or not and filling fraction (the filling fr action applies to intact fluid)

• HydroD will automatically fill out the columns Tank Lc no and Compartment name (this has been defined earlier as part of compartment generation.

• Fill in rest of information as follows:


DET NORSKEVERITAS20



of SemiSubmersible

Step 13 in the wizard• HINT

� You may document by using colour coding as shown

� And apply properties graphically


DET NORSKEVERITAS21



of SemiSubmersible

Step 14 in the wizard• Create a mass model

• The mass model may be specified from a FEM file (i.e. created by GeniE), user specified options or from a Morison model.

• In this case the mass model has been created by GeniE and is found on thefile Structure_T4.FEM

� You find this file fromC:\Program Files\DNVS\HydroD\Examples\Semi or from the project directory if you copied them there


DET NORSKEVERITAS22



of SemiSubmersible

Step 15 in the wizard• Fill compartments to balance buoyancy and mass

• Select filling fluid and compartments as shown below and press “Compute filling fractions” (note that all combinations can be toggled off to speed up the process)

• Filling fractions are now computed by the program ensuring equilibrium

� Click OK to accept the changes to the filling fractions

� The changes are now permanent (and e.g. reflected in compartment contents)


Toggle this off

DET NORSKEVERITAS23



of SemiSubmersible

Step 16 in the wizard• Create flooding openings

• Flooding openings are connected to compartments

� It is also necessary to specify weather tight if performing stability rule check based on MARPOL


DET NORSKEVERITAS24



of SemiSubmersible

Step 17 in the wizard• Make hydrostatic analysis

• Hydrostatic analyses depend on loading conditions and location

� In addition you may decide upon start and end of angle interval where you want to compute


DET NORSKEVERITAS25



of SemiSubmersible

Step 18 in the wizard• Add wind profile

• Wind influences stability as heeling moments and it is thus necessary to include it in the stability calculations.

� The wind contribution is a combination of wind profile, drag coefficients, block coefficients and active structure area.

• Wind profiles may be user defined or standard IMO MODU Wind Profile

� This tutorial assumes usage of standard wind profile, using wind velocity of 75 m/s

� The wind profiles may be edited from the browser as indicated below


DET NORSKEVERITAS26



of SemiSubmersible

Step 19 in the wizard• Create drag coefficients

• Specify the drag coefficient curve as a relation between diameters and drag coefficients.


DET NORSKEVERITAS27



of SemiSubmersible

Step 20 in the wizard• Create drag block coefficients

• Specify the drag block coefficient curve as a relation between cross sectional block coefficient and drag coefficients.


Drag as function of cross-sectional area divided by circumscribed area (i.e. is it a round shape or is it something more square

DET NORSKEVERITAS28



of SemiSubmersible

Step 21 in the wizard• Create the heeling moment

• The heeling moment is now defined as a combination of:

� This heeling moment is perpendicular to the heeling axis

• You may also specify the wind heeling moments by a user definition

� This tutorial assumes empiric flow as defined above


DET NORSKEVERITAS29



of SemiSubmersible

Step 22 in the wizard• Create the hydrostatic analysis run

• And execute it......

• It is possible to make changes in the workspace while the activity monitor is running. This should however be done with caution since one or more running activities mayactively be using the settings in the objects.


Notice that you may run multiple activities in separate threads(exploiting multiple processors)

DET NORSKEVERITAS30



of SemiSubmersible

Step 23 in the wizard• Look at the report

• The report documents the critical information that is needed for engineers to document safety or not.

� Some examples on how to assess the information is given in the following

• GZ-curves


DET NORSKEVERITAS31



of SemiSubmersible


• Moment of force

� Notice that you have an efficient tool for manually computing the area under/between the curves (for manual checking) by altering the start and stop angles, the example below shows that righting moment has been found for the area corresponding to 0 to 35 degrees


DET NORSKEVERITAS32



of SemiSubmersible


• Openings

� As can be seen the opening will be adjacent to the sea surface at heeling angle 52 degrees

� There may be several openings in the analysis


DET NORSKEVERITAS33



of SemiSubmersible


• Detailed information

� There is also additional information needed to document safety, this may be found under the “Information” tab.


DET NORSKEVERITAS34



of SemiSubmersible

Step 23 in the wizard• In addition to investigating results from the standardised report, you may also make

your own report as follows:

� This report will give the most extensive amount of information

� Notice you may make it for Html viewing or using MS Word or MS Excel (you need to have Microsoft versions 2003 or later)

� Below is shown an example using Html as viewer


DET NORSKEVERITAS35



of SemiSubmersible

• To compute still water forces and moments you need to specify at which cross sections the program shall compute these.

� Open up the browser as indicated below

� Delete the existing cross-section as defined when stepping through the wizard, i.e. LoadCrossSection1.

� Define 20 cross-sections spanning from -50meters and +50 meters in X-direction

Part 2 – Modifying cross sections

DET NORSKEVERITAS36



of SemiSubmersible

• Cont’d


DET NORSKEVERITAS37



of SemiSubmersible

• Re-run the crossections analysis to see the forces and moments

� Easiest to start analysis again from browser

• Investigate the forces and moments

� Open up from the browser as shown

� See next page for examples


wang.rong

Text Box

go to Stability Analysis and RMB the Stability analysis 1

DET NORSKEVERITAS38



of SemiSubmersible

• Forces


DET NORSKEVERITAS39



of SemiSubmersible

• Moment

• You may look at other forces or moments, e.g. moments around x-axis and y-axis at the same time....


DET NORSKEVERITAS40



of SemiSubmersible

• In this Part you will define 3 new loading conditions.

� Loading condition 2 is a copy of loading condition 1, but the draft is changed so that z water level is moved from +15 to +10m. Automatic filling of compartments is used to achieve equilibrium.

� Loading conditions 3 and 4 are copies of loading conditions 1 and 2 respectively – in addition some of the tanks are flooded. Equilibrium is now achieved by using the existing tank fillings and the program is thus adjusting draft, trim and heel to ensure equilibrium

� Note: When copying a loading condition, the resulting name will be a variation of the original name, e.g. LoadingCondition1_1is a copy of LoadingCondition1

• Make loading condition 2 (=LoadingCondition1_1)

� Copy from LoadingCondition1

Part 3 – Additional loading

conditions

DET NORSKEVERITAS41



of SemiSubmersible

• Modify LoadingCondition1_1

� Change the z-water level to +10m

• Use the automatic compartment filling to achieve equillibrium between mass and buoyancy

� Select all pontoon compartment contents

� Deselect “Analyze all combinations” and press “Compute filling fractions”

� Press “OK” to apply the filling fractions to the model


conditions

Activate from browser

DET NORSKEVERITAS42



of SemiSubmersible

• Make loading conditions 3 and 4

� Copy loading condition 1 to loading condition 3 and 2 -> 4 using same copy/paste techniques as shown on page 40.

• Make compartments flooded in Loading Condition 3 (=LoadingCondition1_2)


conditions

DET NORSKEVERITAS43



of SemiSubmersible

• Make compartments flooded in Loading Condition 1_2

� Specify that compartments 9 and 23 are flooded

• Find new equilibrium for Loading condition 1_2


conditions

DET NORSKEVERITAS44



of SemiSubmersible

• Find new equilibrium for Loading condition 1_2

• A new draft, trim and heel is now computed


conditions

DET NORSKEVERITAS45



of SemiSubmersible

• Modify Loading Condition4 (=LoadingCondition1_1_1)

� Add flooding to compartments 2 and 22 (same approach as for LoadingCondition3)

� Compute a new equilibrium position similar as for LoadingCondition3


conditions

DET NORSKEVERITAS46



of SemiSubmersible

• Create new hydrostatic analysis

� Make new hydrostatic analysis as follows

� Remember that loading conditions 1_2 & 1_1_1 represent damaged conditions


conditions

DET NORSKEVERITAS47



of SemiSubmersible

• Add wind heeling moment to the hydrostatic analysis no. 2, 3 and 4 by copying the heeling moment curve from HydroStatics1:

• and continue pasting into HydroStatics3 and 4


conditions

DET NORSKEVERITAS48



of SemiSubmersible

• Run all the new analyses

� No need to re-run analysis 1

• You may look at new results from browser


conditions

DET NORSKEVERITAS49



of SemiSubmersible

• Check the structure for compliance with NMD (Norwegian Maritime Directorate) and IMO Modu for loading conditions 1 – 4 (one should note that connecting the flooding opening to compartments is not normally done when checking against IMO MODU)

� Remember that loading conditions 1 & 2 represent intact conditions

� Similarly, loading conditions 3 & 4 simulate damaged conditions since some of the tanks are flooded

• Make hydrostatic rule checks as follows

Part 4 – Hydrostatic rule checks

DET NORSKEVERITAS50



of SemiSubmersible

• Check the results

� You may check the results individually and on the fly from the browser

� Alternatively, you may make a report containing results from all hydrostatic rule checks

� Both options are shown in the following


DET NORSKEVERITAS51



of SemiSubmersible

• Check the results (cont’d)


DET NORSKEVERITAS52



of SemiSubmersible

• Define the allowable vertical center of gravity analysis

� Access dialog from the browser

� Specify rule sets for intact and damaged conditions

� Specify algorithmic parameters

� Select hydrostatic analysis and press OK

Part 5 – AVCG analysis

DET NORSKEVERITAS53



of SemiSubmersible

• Define the heeling moment of the allowable VCG analysis

� Access dialog from the browser

� Use the curve from the hydrostatic analysis

� Press OK


DET NORSKEVERITAS54



of SemiSubmersible

• Execute allowable vertical center of gravity analysis

� Access the activity monitor from the browser

� Press Start and run the analysis


DET NORSKEVERITAS55



of SemiSubmersible

• Look at allowable vertical center of gravity graphs

� Access the graphs from the browser

� There is one graph for each criteria in the intact and damaged rule sets

� In addition there is a min curve showing the smallest permissible VCG value from all the critera


DET NORSKEVERITAS56



of SemiSubmersible

• Look at allowable vertical center of gravity information

� Access the information from the browser

� Expand the tree in the left window pane

� Select one of the criteria and see the listing of the allowable VCG values together with the critical axis and the hydrostatic analysis that gave the allowable VCG value


DET NORSKEVERITAS57



of SemiSubmersible

Make a clean journal file• Save the work for later use

� When save or exit, all data is stored and you can open the workspace later on

• Save the journal file for later use

� You can import the journal file created during this session into a new workspace. This file contains all historical data such as copy, rename and so on.

� It is recommended to make a “Clean Journal file”. This journal file will create a minimum of commands to regenerate the current workspace.

� From the File|Save Clean JS please give the name Semi_Submersible_Stability_in.

� You can look at this file – it is stored on the project directory specified by you.

� The file may be edited and re-used in other projects

Part 6 – Save the work

Date post:	26-Dec-2014
Category:	Documents
Upload:	rong58
View:	491 times
Download:	5 times

HydroD Semisubmersible Stability

Documents