SESAM USER MANUAL GeniE Tutorial - HVL

SESAM USER MANUAL

GeniE Tutorial

Modelling a semisubmersible – panel, Morison and structural (FE) models

SAFER, SMARTER, GREENER

Sesam User Manual GeniE Tutorial - Modelling a semisubmersible – panel, Morison and structural (FE) models Date: 13 March 2011 Valid from GeniE V6.3 Prepared by DNV GL - Software E-mail support: [email protected] E-mail sales: [email protected] © DNV GL AS. All rights reserved This publication or parts thereof may not be reproduced or transmitted in any form or by any means, including copying or recording, without the prior written consent of DNV GL AS.

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Sesam User Course – GeniE Workshop: Modelling a semisubmersible – panel, Morison and structural (FE) models

• The purpose of this workshop is to create a concept model and make a panel model, a

Morison model and a structural (FE) model for use in hydrostatic, hydrodynamic and

subsequent structural analysis.

• The focus is primarily to show how different models can be made and not on modelling

details.

• It is assumed that the user is familiar with the modelling capabilities of GeniE – if not, you

should go through the tutorials showing how to make a tubular joint and a semi-

submersible pontoon.

• The user should also be familiar with GeniE’s user interface; this workshop does not

explain in detail how to make the model. The user interface can be learnt from the basic

tutorials as well as other more advanced tutorials.

• The workshop is also accompanied with input files for GeniE (Journal file)

The journal file will create the concept model and the various analysis models

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

colour coding.

All pictures have been

created using

“paper background”

Default viewing settings

have been modified

• The structural data as well as

the loads are fictitious

• This tutorial has been revised with

GeniE version V6.3 – it may

be that you need this or a later

version to complete

this workshop.

You also need access

to the program extension

for curved structure

modelling


• Use the following consistent set of units as database units:

Newton (N), meter, second, kilogramme (kg)

• The main dimensions are given on page 4.

• Detail dimensions are given with the hints.

• Two types of material are used (let thermal

and damping coefficients be zero):

Steel: yield strength = 2.0E8 Pa,

= 7850 kg/m3, E = 2.1E11 Pa, = 0.3

SuperMaterial: yield strength = 2.0E8 Pa,

= 1780 kg/m3, E = 2.1E11 Pa, = 0.3

» This material is for the very thick plates and shells used for most of the structure. Thick plates with low density material are used to represent stiffened plates.

» Remember to set Supermaterial as the default material.

• Cross sections used:

Pipe1: pipe with diameter = 2 and

thickness = 0.1 (used for braces

between columns)

Pipe2: pipe with diameter = 1 and

thickness = 0.05 (used for derrick)

Pipe3: pipe with diameter = 0.8 and

thickness = 0.04 (used for derrick)

Cone1: a cone section with ‘dynamic

thickness’ = ‘largest’

Before you start – specify the properties

• Use Edit > Properties to define a) Materials b) Cross sections c) Plate thicknesses


Girder: a T-section modelled by using an

un-symmetrical I-section with data:

single symmetric, height = 0.8,

web thickness = 0.04,

top flange width = 0.06,

top flange thickness = 0.05,

bottom flange width = 0.5,

bottom flange thickness = 0.05

(The top flange width is marginally

bigger than the web thickness.)

Stiffener: an L-section with

height = 0.6,

width = 0.3

and both thicknesses = 0.04

Remember to set this section as default

• Plate thicknesses used:

Th03: thickness = 0.03



Set Th50 as default

• The semisubmersible is fixed at three support

points. These fixations are required to ensure

the equation system is non-singular.

• Follow the hints:

Create geometry of pontoon and column, page 5

Create panel model (T1.FEM), page 19

Create the full model, page 23

Create Morison model (T2.FEM), page 27

Create derrick, page 28

Create compartments, page 30

Create equipments, page 33

Create supports and structural model (T3.FEM), page 35

Exercise in mesh refinement, page 36


Pontoon height and width

Column width at base

Pontoon cross section


Create geometry of pontoon and column

• Insert a guiding plane with data as given below. The resulting guide plane is shown next

page. This guiding plane at Z = 0 is at the top of the pontoons.


origin

1

2

3

• Insert a guide line by clicking the Guide line button:

• Insert a guide arc by selecting

Elliptic Arc from Center and Two Points:

When creating the arc notice the help text

in the lower left corner. The result is shown below.


• Copy the two guide curves by a mirror operation about the plane Y = 27.36. Note that any

point (coordinate set) in the mirror plane and any vector normal to this plane may be used.

The result is shown below.

• Copy the four guide curves a distance of 3.75 down. This is where the pontoon starts to

curve (bilge top).

Y = 27.36


• The lower part of the pontoon (bilge) curves (cylindrically and spherically) down to a flat

bottom. Create curves describing the extent of this flat bottom. Do so by creating the guide

curves in the guiding plane at Z = 0 followed by moving them down a distance of 7.5.

Below is shown the four guide curves in the guiding plane at Z = 0. (Curve11 and

Curve12 are mirror copies of Curve9 and Curve10.)

Below is shown the four guide curves after moving them down a distance of 7.5.


• Create vertical lines for the vertical sides of the pontoon as shown below.

• To create the cylindrical and spherical lower parts of the pontoon we need arcs in vertical

planes. To create these arcs we need centre points. By copying two of the curves enclosing

the flat bottom of the pontoon (Curve9 and Curve10 on previous page) up a distance of

3.75 we get a line through these centre points. These two ‘centre-point-curves’ (Curve18

and Curve19) are shown below.


• The five arcs may now be created. Two of them (Curve23 and Curve24) by mirror copying.

• Before creating surfaces set default material to SuperMaterial and default thickness to

Th50.

• The four vertical sides of the pontoon (see below) are created

by skinning operations. Shift the Flat Plate button to

Skin/Loft Curves button and depress it.

• Then click the upper curve once and the lower curve twice

(e.g. Curve1 - Curve5 - Curve5 below) for each of the four

surfaces. (Clicking the same curve twice closes the skinning.)


• The lower curved surfaces of the pontoon (the bilge) are

created by sweep (extrude) operations. (The cylindrical

surfaces may alternatively be created by skinning between

the two arcs.) Shift the Flat Plate button to Sweep Curve

Dialog button and depress it.

• Then click the curve (profile) to sweep and then the curve

forming the sweep path. E.g. Curve20 and Curve5 below.

• Create the rectangular and flat top surface of the pontoon by skinning between Curve1 and

Curve3.

• Note that depending on the way you create a surface you may need to flip the surface

normal. The colour tells which surface is facing you: bluish for positive local z, reddish for

negative. Check the surface normal for each surface you create.


• To cover the 180 degree sector of the top surface create first a guide line (Curve25) as

shown.

• Then create the surface by a cover operation:

Select all curves enclosing the surface, then

use the context sensitive menu (right-clicking)

and select Cover Curves as shown to the right.

• The result is shown below.


• To create the rectangular and flat bottom surface as well as the 180 degree sector of the

bottom surface do a similar operation as above. The guide curve needed is labelled and the

surfaces to create are highlighted below.

• Now create a longitudinal

bulkhead. To do so, first

create the four guide lines in

the centre plane shown to the

right. Two in the top and two

in the bottom surface. These

may be created by copying or

through dialogs:

Insert > Guiding Geometry > Guide Line Dialog.

• The bulkhead consists of

two parts. The rectangular

part may be skinned.

• The surface with a curved

corner may be created by

a cover operation. This

requires a vertical guide

curve as shown to the right.


• Create the transverse bulkhead shown to

the right by a cover operation. Select the surrounding

guide curves, RMB and choose “Cover”

• Make three copies of the

transverse bulkhead as shown

to the right. The copies are at

the following distances from

the original: 4.94, 14.94

and 32.3, all in negative

X-direction. (The last copy is

at X = 0.)

• Now we will create the column-pontoon intersection. For this

we will use a new guide plane with data as shown below

(plane is at Z = 0). There is only one spacing in both

directions. The new guide plane is shown to the right.

Hint: Remove GuidePlane1 from the view to see the new

• First create two new guide lines as shown above and then use Guiding Geometry> Conic

Sections>Circular Fillet to round off the corner with radius 2 as shown below.

new guide plane

two guide

lines

fillet

r = 2


• The next task is to create the column.

From elevation Z = 7 and up the column

is cylindrical. Create a guide plane at this

elevation with data as shown to the right.

(The guide plane will later be moved up

to the deck elevation and used there.)

• Use the guide plane to create an arc as

shown at the bottom of the page (A).

• Do a skin operation to create a quarter

of the lower part of the column as shown

below (B).

A

B


• Create the 90° sector of the vertical column to the right by

Insert > Plate > Sweep Curves Dialog, selecting the

highlighted arc as curve to sweep and entering a sweep

vector equal to the height of the cylinder (26.5) as shown.

(Remember to select the arc prior to using the pulldown menu)

• Copy the 90° sector of the conical transition

plus the 90° sector of the cylinder plus the 90°

arc three times by a copy-rotate operation.

Remember that you may click in the model to

fill in points and vectors in the Copy dialog.

The resulting structure is shown to the left.

The guide planes have been removed

from the display by right-clicking the

guide plane filter button and closing the

eye as shown below.


• Move the guide plane at

elevation 7 up to the lower

deck at elevation 25.5, i.e. 18.5 up.

Then copy this guide plane up to the

upper deck at elevation 33.5,

i.e. 8 up. The result is

shown to the right.

• Create an internal bulkhead for the

column by first creating a plate

extending outside the column and

then trimming this. Create e.g. a

bulkhead as shown to the right by

pressing the flat plate button

and clicking the four corner points.

The idea here is simply to use

existing points to make the plate

wide enough in the horizontal

direction. Then select and right-click

the plate to Divide it through the

dialog below.

1

2

3

4


• The division

creates three parts.

Select the two parts

outside the column

as shown to the right

and delete them.

• After the deletion

only the bulkhead inside

the column remains. Copy this

by rotating it 90° about the column

axis to create a bulkhead in the

Y-direction. The result should be as

shown to the right.

• The geometry of pontoon

and column is now complete.


Create panel model (T1.FEM)

• We need to divide also the two top surfaces of the

pontoon into smaller parts as only the parts outside

the column-pontoon intersection are wet surfaces

and shall receive hydrodynamic loads.

• After selecting the two surfaces, dividing them

and thereafter selecting the top wet surfaces the

result should be as shown to the right.

• Select all wet surfaces (those subjected to water)

and put them into a named set “Wet_surfaces” as

shown to the right.

• Use Edit > Properties and go to the

Mesh Property tab to create a mesh

property with Element Length = 5.

• Assign this mesh property to the new set.


• Use Edit > Properties and go to the Wet Surface

tab and create a wet surface property (the

property holds no data).

• Assign the wet surface property to

the set “Wet_surfaces”. Provided that all surface normals

points outwards select the Front side as shown below.

(A consistent definition of surface normals is essential.)

• Use Loads > Load Case to create a

dummy hydro pressure referring to

the wet surface property, see below.


• Create a mesh for the wet surfaces only. To do

so an analysis activity need to be defined.

(Meshing with no analysis activity will create

a mesh for all surfaces and beams. The activity

created will not be run, it is only for meshing.)

Right-click the Activities folder as shown

below to create a new analysis activity.

• Then find the analysis activity in the browser

and right-click the meshing activity to edit it

as shown below.


• In the Mesh activity dialog shown to the lower right select Mesh Subset and select the set

containing the wet surfaces as. Make sure the Superelement Type is set to 1.

• Use Tools > Analysis > Create Mesh (or Alt+M) to create the mesh shown to the lower left.

• Creating a panel model is

concluded by exporting

the model by:

File > Export > FEM File

• The file name will take its

name from the name of

the workspace appended

with T1.FEM. Remove

the workspace name so

that the exported file is

T1.FEM.


Create the full model

• The panel model (T1.FEM) has now been created. The models yet to create are the:

Morison model (T2.FEM)

Structural FE model (T3.FEM)

• Before creating the deck plates set the default thickness to Th35.

• Then create horizontal plates of the deck structure as shown below.

• For the three plates of the top deck – but only these three – change the thickness and

material to Steel and Th03, respectively. (Only these plates will have girders and stiffeners

and shall therefore have normal material and thickness.)

• Create the vertical plates of the deck structure. Three vertical plates in both X-direction and

Y-direction. The plates stop at the column cylinder wall (there are already vertical plates

inside the column).

First create the

three plates of

the lower deck and

then copy the three

surfaces up to

the upper deck.


• Create a circular horizontal plate inside the

column at elevation 7 by a cover operation,

i.e. select all four arcs enclosing the plate

and then right-click them to cover them.

• Copy this circular plate up to elevation 25.5

(lower deck). Notice that the 90° sector

overlapping the existing plate of the deck

will not be copied, i.e. only 270° of the 360°

circular plate will be copied.

• Then copy the circular plate up to elevation

33.5 (upper deck).

• The result is shown to the right.

• Set default material to Steel.

• Create girders and stiffeners in the top deck. The girders in Y-direction are positioned as

shown. The 9 stiffeners in the X-direction are evenly spaced over the deck width of 27.36,

i.e. a spacing of 2.736. The stiffeners may e.g. be created through a dialog and clicking

points as if the beam is at the edge and then adjusting coordinates to shift it sideways.


• The three stiffeners encircled

on the previous page must be

shortened so as not to

extend into the open area

in the deck. Select a beam,

right-click to edit it and

in the Edit Beams dialog

go to the Move End tab.

Click the end to move

and then the point to

where it shall move

while making sure

‘as point’ is selected.

• Repeat the process for

the other two beams.

The result is shown

below.

• The girders and stiffeners now

need to be given offsets

(eccentricities) so as to be

welded underneath the plates.

• Select all beams and edit them.

In the Edit Beams dialog go to

the Offset Vector tab and flush

the whole beam at top.

The result is shown to the

right.


• A quarter of the model is now complete. Copy this quarter by mirroring it

about origin in X-direction. Do so by first switching to the

‘Modelling - structure’ display configuration and then selecting the quarter

model by dragging a rubberband.

• Right-click the model to copy it. Go to the Mirror tab and enter data as shown below. The

Preview check box verifies the position of the copy before executing the operation.

• When executing the copy operation a warning appears saying that a couple of surfaces

cannot be copied. These are surfaces in the mirror plane and copies would come on top of

the originals which cannot be accepted. Click OK to the warning.

• Make a full model by mirror copying the half model about origin in Y-direction as shown

below. Again click OK to the warning about surfaces that cannot be copied.


Create Morison model (T2.FEM)

• The columns are connected by two horizontal braces. These are modelled as beam elements

with section Pipe1 and material Steel. Steel will be the material to use for the remaining

structure so this material may as well be set as default. The braces connect with the

columns at the top of the conical transition as show below.

• Export the Morison model as superelement number 2. Use Edit > Rules > Meshing to set

the superelement number. The name of the exported file should be T2.FEM.

• See earlier in this workshop for how to define a set “Morison” (this time containing the two

braces only) and create a mesh for this set only. For meshing the braces no mesh density is

required (the minimum default density will give two beams).


Create derrick

• Now create the derrick as shown below. Use the sections Pipe2 and Pipe3 and follow the

guidance on the next page

El. 46m

El. 55m

El. 65 m

El. 38.5 m


• Start by the

lower vertical legs with section Pipe2

and height 5. Continue by the sloping

legs. These beams may be copied

by mirroring or you may find it

more convenient to create them

in a more direct manner.

• Then create the

remaining part of

the derrick. All with

section Pipe3 except

for the four short top

horizontal beams at

elevation 65 that

are Pipe2.

• Use the snap plane

to insert the horizontal

bracings at Z = 46 and 55.

• Put all beams of the

derrick into a named

set. This facilitates

selecting these beams

for use at a later

stage.

• Add four mass points at top of the derrick as

shown to the right, each mass point has a

mass of 2.0E5. You may use the command

Insert > Mass

X: 6.04151

Y: 4.20755

Z: 55

X: 10.5789

Y: 7.09434

Z: 46

1 2


Create compartments

• The pontoons have ballast

tanks filled with water. These

are created as compartments

in GeniE and taken into

account in the subsequent

hydrodynamic analysis in

HydroD/Wadam.

• Use Loads > Compartment >

Compartment Manager

to open the Compartment

Manager dialog and click OK.

• By this action GeniE will

search for all closed

compartments in the entire model and list these in the Compartments folder (underneath

the Analysis folder). Note that the Default display configuration displays the compartments

in a brownish colour. Also note that clicking the plate selection button ( ), i.e. lifting it

to make plates unselectable, allows selecting compartments by clicking. There is also a

predefined view “Compartments” that shows compartments only.

Three compartments highlighted


• Note 1: HydroD/Wadam requires that a separate

load case is defined for each compartment to be

considered. Furthermore, these load cases should

be numbered consecutively after the dummy

hydro pressure load case for the outer water pressure

(in this workshop: load case 1, LC1).

• Note 2: These compartment load cases should

not pertain to any particular analysis activity.

Right-click the Analysis > Load Cases folder

to make this folder active (rather than an

analysis activity).

• We want the four pontoon compartments

shown to the right identified as

compartments (tanks) so as to contribute

to the analysis in HydroD/Wadam.

The procedure will be:

Insert a new load case (this will

then be current). Do not check

Dummy Hydro Pressure.

Select a compartment and right-click it

in the browser to open the Properties dialog.

1

2

3

4

LC3

LC2

LC4

LC5


In the Compartment

Loads tab of the

Properties dialog position

the mouse over the

vertical text Intensities

and see that new options

are revealed.

Select Dummy Hydro

Pressure from the pull-

down menu as shown to

the right and click OK to

accept the data and close

the dialog.

Right-click the load case

(LC2 – LC5 in the Load

Cases folder) and generate

applied loads.

After this you should see

orange load arrows as

shown to the right (using

Modelling - Transparent

display configuration) for

each compartment load

case.


Create equipments

• An equipment (a tank, a generator or other)

of mass = 15000, height = 4, length = 3

and width = 5 shall be defined.

Use Loads > Prismatic Equipment

• An equipment is positioned in the context

of a load case, read the following text on

this and next page

including the point about Wadam

before commencing the positioning.

• This equipment shall be positioned

symmetrically in four positions as shown

to the right. The lower figure shows the

equipment in the positive X-Y quadrant.

The exact position of the equipment in

this quadrant is (20,20,33.5). Right-clicking

an equipment and selecting Properties

allows such exact positioning.


• Having placed one of the equipments

select it and right-click to place a copy.

Each copy must be positioned exactly.

• The hydrodynamic analysis in Wadam requires the equipments represented as mass rather

than line loads. Such mass will be independent of the load cases, yet we must position the

equipments within a load case and thereafter select to represent the equipment as load case

independent mass. The equipments will then ‘be taken out of the load case’. Let us use the

last compartment load case LC5 for the equipments. See below.

Exact location shown here by editing the

position from the equipment’s property dialogue box


Create supports and structural model (T3.FEM)

• Even though the semisubmersible is floating

the FE model must be supported against

rigid body displacement or else the structural

analysis will fail (it will be singular). These

supports will have no effect on the

hydrodynamic analysis in Wadam. The

reaction forces should be zero in these

supports so it is not that important where

they are positioned as long as they support

the structure in a statically determined way.

The support shown to the right is adequate.

The fixed dof’s are shonw – all others are free.

• Use Edit > Properties and go to the Mesh Property tab to create a new mesh property with

Element Length = 3. Assign this density to all plates/shells, i.e. to the whole structure

except the beams. Note that you can go to the Utilities > Sets folder, select the two sets for

the Morison model and the derrick and use Alt+Minus to remove these sets beams from the

display. Then you can use a rubberband to select the remaining model, i.e. the plates/shells.

• Create the FE model and export the model as file name T3.FEM. Change superelement

type from Edit Rules > Meshing. This time no analysis activity is needed since a mesh for

the whole model will be created. The mesh will be as shown below. The eccentric masses

of the equipments

and the mass points on top of the derrick appear

as yellow dots.

• It should be noted that the FE mesh is rather

coarse and far from perfect. In a real

analysis a finer mesh should

be used and efforts should

be put into improving

element shapes. The

subsequent pages deal

with this subject.

Fix X, Y

and Z Fix Z

Fix Y and Z


Refine mesh for a quarter model (meshing exercise only, not to be analysed)

• Meshing (Tools > Analysis > Create Mesh or simply Alt+M) without any mesh control data

produces the mesh shown below to the left. This is a minimum mesh determined by

intersecting plates and stiffeners and is obviously a totally unacceptable mesh.

• Using Edit > Properties, the Mesh Property tab, to create a new mesh property with

Element Length = 3 and assigning this to all plates/shells as explained on the previous page

produces the mesh shown below to the right. This mesh is better though still rather coarse.

• Defining a new mesh property with element

length = 1 and assigning this to the conical

part of the column as well as the neighbouring

horizontal plates may give a refined mesh for

this critical region as shown to the right. Note

that you need to split (right-click and select

Divide) the horizontal top plates of the pontoon

in order to give different mesh data for different

parts of these plates.

• Peeling off plates

(Alt+minus) may,

however, reveal a

poor internal mesh

as shown to the right.


• To improve the mesh step-by-step select plates, create new mesh properties if necessary

and assign these to the plates. Use Alt+M to create a new mesh. Note that you can select

plates while displaying the mesh as shown below, i.e. you do not have to display the

geometry model. And Alt+M will irrespective of the current display create a mesh for the

complete model. This makes refining the mesh a fairly quick and easy process.

• Focusing in on the plate shown below we find

a triangular element that we would like to get rid of.

We therefore want to increase the number of elements on the top edge from 8 to 9. Double-

click the plate to highlight the plate edges. Select the edge shown below and create a

feature edge there. (The top plate edge is split in two because of the conical transition wall.)

• Double-click to return to normal view mode and select the feature edge. To do so lift plate

selection button and press feature edge selection button . Create a mesh property

being 8 number of elements and assign this to the feature edge. The top edge will then have

8+1=9 elements as shown below to the right.

3. Alt+M

1.

2.

4.

1.

2.

3.

4.


• Continue refining the mesh by:

Creating more mesh properties (folder Properties > Mesh) of type

» Mesh density

» Number of elements

Assigning these to:

» Plates

» Plate edges through creating feature edges

• Note that you may highlight

edges of several plates by

clicking a plate, shift-clicking

more plates and finally

shift-double-clicking a last plate.

The result may be as shown to

the right.

• If necessary you may also use Edit > Rules > Meshing to define some general meshing

rules, i.e. rules applying to the whole model.

• You may also create mesh options (Edit > Properties > Mesh Option tab or right-click the

folder Properties > Mesh Options) and assign these to specific plates.

• Finally, when satisfied

with the mesh for a plate

you may lock it. This

means that a change of

mesh settings for other

plates will not alter the

mesh of locked plates.

• Continue playing with mesh settings until you get the grip of it.

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