Introduction to OrcaFlex 2: the objects

you are watching one of a series of

videos giving an introduction to

orcaflex

the first four of these videos which

we've called the fundamentals

are those that we would regard as

prerequisites for looking at any of the

other subsequent topics

if you are already familiar with these

fundamentals you may want to pick and

choose the subsequent videos you watch

based on your area of interest

if you're a complete beginner with

orkaflex i would strongly encourage you

to watch the full series in order

as this will give you a good basic

overview of the program

how to navigate it and where to access

and input data

it goes without saying that the quality

of any orthoflex analysis

is only as good as the quality of the

input data

and that of course relies on the skill

and experience of you

the user these videos will help you to

learn how to use orkaflex as one of your

analysis tools

and i do hope that you find them

educational and maybe even a little bit

enjoyable too

the focus of this next session will be

the orgaflex objects

orkaflex is made up of nine modular

building blocks or

objects while later videos will look at

the objects in detail you will now be

introduced to each of them

looking at their application the types

of data input needed and how they can

form part of a full model

the objects available are the vessel

the line the 6d boy

the 3d boy the winch

the link the shape

the constraint and the turbine

the objects are named based on their

primary application although it's

important not to let this limit your

thinking

for example boys are not just used for

modelling floating buoys but can also be

used to apply mass at a specific point

to represent anything from a crane hook

to a subsea manifold

likewise the winch isn't just for

modelling winches but can be used when

something needs to dynamically change in

length

so taking a look at the vessel object

this is typically used as you might

expect

to model things like ships barges large

floating platforms

or as in this case fpsos

however it can more widely be used for

anything that requires diffraction data

associated with it

or something that needs to move in a

prescribed direction over the course of

a simulation

the vessel is a rigid body whose motion

can be determined by the user in a

number of ways

including response amplitude operators

or raos for the six degrees of freedom

first order wave load reos and second

order wave drift qtfs

and it can also be driven around the sea

surface with user-specified velocities

and headings

the raos and qtfs are imported from a

diffraction analysis program

an example of which is orca wave which

is bundled as part of the orkaflex

license

this can also provide the data for

creating the wireframe

and the shaded graphics drawings of the

vessel

next up is the line this is a flexible

linear element

which uses a lumped mass model to

represent things like

pipes flexible hoses cables and mooring

lines

its mass and hydrodynamic properties are

lumped at nodes

which are connected by straight massless

segments

the length of the segments and therefore

the quantity of the nodes are decided by

the user

the greater the number of nodes the more

accurate the line representation

but at the expense of simulation time

and file size

the line properties can vary along its

length

this line for example has three sections

the first and the last are a heavy line

type

and the center section is buoyant

and when we run a static analysis we can

see the center section of the line

is lifted up by that buoyant line type

the line ends can be fixed or free

or connected to other objects in a model

and ends can also be disconnected during

the course of a simulation

take for example this right hand end of

this line which is connected to a vessel

and part way through the simulation that

line end

is released

the contents of a line can also be

modeled as can

additional elements such as buoyancy

modules clump weights

and drag chains all of which are modeled

as attachments

we'll move on now to take a brief look

at the two boy objects

note that although they are called boys

they do not need to be buoyant

you set the level of buoyancy by

inputting a combination of mass

and volume parameters first up is the 3d

boy

this is a simple point body with only

three translational degrees of freedom

and it is represented as a vertical

stick in the 3d view

these are intended to be used to model

objects where you need to introduce mass

but where rotations can be regarded as

insignificant

such as shackles or crane hooks you can

see that the data form is quite simple

and here are the mass and volume

parameters for setting the level of

buoyancy

moving on to the 6d boy this has as the

name suggests

6 degrees of freedom so can rotate as

well as translate

it is intended to be used in the drag

and inertia regime

in which morrison's equation applies i.e

its characteristic dimension

should be smaller than the wavelength it

experiences

there are a few different types

available for different applications

but we'll go on to talk more about this

in a later video

we move on now to the link object which

is a simple straight

massless connection linking two objects

in a model

this can be defined as a tether link

which acts much like an elastic band

taking tension but not compression or

a spring damper link which can take both

tension

and compression next is the winch which

is a massless connection between two

or more objects the connection length

simulating payout

or hall in can vary dynamically through

either length control

where the winch wire length varies at a

user specified rate

or tension control where a

user-specified tension

is applied to the winch wire

the winch can be a simple type or a

detailed type

the latter providing options to input

additional

winch drive properties and inertia

properties

the next object is the shape which is

available in a number of geometry

options and types

the shape options on their own are quite

simple such as this cylinder

or the plane or the cuboid block

or the curved plate but these can be

combined

to create some quite complex compound

shapes

they can be used as an elastic solid

type to create physical boundaries for

other objects

they can be used for trapped water areas

which are shielded from the waves such

as moon pools

and they can also be used as drawing

shapes purely for visualization purposes

and there's a further type called the

label which is used for the purpose

of adding text labels to the wireframe

3d view

we move on now to the constraint object

whilst not very interesting to look at

it is after all just a set of axes in

the 3d view

this is arguably the most versatile of

orkaflex objects

it has no physical properties itself but

allows for the customizing of

connections between other objects it has

two frames of reference

one connected to a parent object and the

other connected to one or more child

objects

it can allow degrees of freedom to be

introduced between parent and child

objects or to have imposed motion

defined

the constraint has a wide variety of

potential applications

such as crane modelling which uses a

number of constraints chained together

in series

wave energy converters pipelace stingers

jacket launch simulations

calm boys and turret moored fpsos

remember though that the constraint is

so versatile there will be many use

cases for it that we haven't even

considered yet

in fact when we first introduced

constraints to our users in 2016

we demonstrated how a combination of

calculated and imposed motion

constraints could be used to create a

bicycle model

the final object in the orkaflex suite

is the turbine

this is used for modelling horizontal

axis wind turbines and includes

dedicated models for the generator

gearbox hub and blades

the blade model is similar structurally

to the line model being a beam element

split up into nodes and segments

it can be fixed or flexible to capture

aero elastic coupling effects

and the aerodynamic loads are captured

using a blade element momentum

or bem method

turbine object allows for a floating

offshore wind turbine analysis to be

performed entirely within orca flex

so that's an introduction to all of the

orca flex objects

in the next video we'll look at how some

of these can be combined as we begin to

build an orca flex model

hopefully you'll have found this to be a

useful introduction to the modeling

objects available in orkaflex

the next video in the series will look

at creating a data file

you