OrcaFlex Manual - Orcina

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System Modelling: Data and Results, 6D Buoys 388 w the number of cylinders and their lengths and diameters. A conical or spherical shape can be approximated as a series of short cylinders of gradually increasing or diminishing diameter. Spar Buoys model surface-piercing effects in a much more sophisticated way than Lumped buoys. Effects such as heave stiffness and righting moments in pitch and roll are determined by calculating the intersection of the water surface with each of the cylinders making up the buoy, allowing for the instantaneous position and orientation of each cylinder in the wave. Slam forces are also calculated and applied separately for each cylinder. Hydrodynamic loads on Spar Buoys are calculated using Morison's equation. Added mass and drag forces are applied only to those parts of the buoy which are in the water at the time for which the force is calculated. For partly immersed cylinders, added mass and drag are scaled according to the proportion of the cylinder volume that is submerged. The use of Morison's equation implies that the buoy diameter is small compared to the wavelength (usually the case for CALM buoys and the like) but means that some load terms are not represented. Towed Fish The third type, called Towed Fish, are intended for modelling bodies, such as towed fish, whose principal axis is normally horizontal. Towed Fish buoys are identical to Spar Buoys except that the stack of cylinders representing the buoy is laid out along the x-axis of the buoy, rather than along the z-axis. Because they are modelled as a stack of concentric cylinders, Spar Buoys and Towed Fish are less suitable for fully submerged objects with more complex geometry. For further details see Spar Buoy and Towed Fish Properties. 6.9.1 Wings 6D buoys can have a number of wings attached; these are useful for representing lift surfaces, diverters etc. Each wing has its own data and results available. A wing is a rectangular surface, attached to the buoy at a specified position and orientation, which experiences lift force, drag force and drag moment, due to the relative flow of fluid past the wing. These loads depend on userspecified coefficients that depend on the incidence angle of the relative fluid flow. The fluid referred to here can be the sea, the air, or both, as follows. � Whenever the wing is completely below the instantaneous water surface, then the lift and drag loads are calculated using the sea density, velocity and incidence angle. � Whenever the wing is completely above the water surface, and if you have selected to include wind loads on wings (on the Wind page on the Environment data form), then instead air lift and drag loads are calculated and applied, using the same formulae and coefficients, but using the air density, velocity and incidence angle. � When the wing is partially submerged, OrcaFlex calculates what proportion of the wing rectangle area is below the instantaneous water surface, i.e. its 'proportion wet' PW. OrcaFlex then calculates the water lift and drag loads as if the wing was fully submerged, but then scales them by PW before they are applied. In addition, if you have selected to include wind loads on wings, then OrcaFlex also calculates the air lift and drag loads (as if the wing was not submerged) and scales them by 1-PW, i.e. the 'proportion dry', before they are applied. When this happens, therefore, both water and air lift and drag loads are applied, each appropriately scaled. The wing lift, drag and moment results then report the water loads whenever the wing is more than half submerged and the air loads whenever it is less than half submerged. Note: The true effects of a wing breaking surface, for instance planing and slamming, are much more complex than this and are not modelled for wings. However slam loads on the 6D buoy itself can be modelled – see Slam Force Theory. Wings do not have any mass, added mass or buoyancy associated with them. Therefore any mass, added mass or buoyancy due to wings should be added into the properties specified for the buoy itself. The drag force on a wing is the force applied in the direction of relative flow. The lift force is the force at 90° to that direction. The moment represents the moment (about the wing centre) that arises due to the fact that the centre of pressure may not be at the wing centre. These loads are applied at the wing centre and are specified by giving lift, drag and moment coefficients as a function of the incidence angle α between the relative velocity vector (flow velocity relative to wing) and the wing plane.
w Chord Leading edge Figure: Wing Model +ve lift Wx Span Wy Wz Principal W Wing Axis -ve lift 389 System Modelling: Data and Results, 6D Buoys Flow Velocity V (relative to wing) Each wing has its own set of local wing axes, with origin W at the wing centre and axes Wx, Wy and Wz. � Wy is normal to the wing surface and points towards the positive side of the wing, i.e. the side towards which positive lift forces act. � Wx and Wz are in the plane of the wing. The wing is therefore a rectangle in the Wxz plane, centred on W. � Wz is the principal axis of the wing. It is the axis about which the wing can easily be pitched, by adjusting the wing gamma angle. � Wx is in the plane of the wing, normal to the axis Wz, so that (Wx,Wy,Wz) form a right-hand triad. � We normally choose Wz and Wx so that Wx is towards the leading edge of the wing. With this arrangement, increasing the wing gamma angle moves the leading edge in the direction of positive lift. We refer to the wing's length in the Wz direction as its span and its width in the Wx direction as its chord. 6.9.2 Common Data All types of 6D Buoy use a local buoy axes coordinate system. The origin of the buoy axes can any point chosen by the user, but the buoy axes directions should be in the directions of the principal axes of structural inertia of the buoy – see Mass Moments of Inertia below. Name Used to refer to the 6D Buoy. Type Three types of buoy are available: Lumped Buoys, Spar Buoys and Towed Fish. The following data items are common to all types. Connection A 6D Buoy can either be Free, Fixed or connected to a Vessel, 6D Buoy or a Line (provided that line includes torsion). � If the buoy is Free then it is free to move in response to wave loads, attached lines etc. In this case the buoy's Initial Position and Attitude are specified relative to global axes. � If the buoy is Fixed then it cannot move. Its Initial Position and Attitude are specified relative to global axes. �
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w Orcina Ltd. Daltongate Ulverston
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Contents 4 w 3.4 Libraries 40 3.4.1
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Contents 6 w 5.6 Dynamic Analysis 1
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Contents 8 w 6.5.23 Wave Scatter Co
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Contents 10 w 8.12 Results 444 8.13
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Introduction, Installing OrcaFlex
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Introduction, Parallel Processing M
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Introduction, References and Links
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Introduction, References and Links
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w 2 TUTORIAL 2.1 GETTING STARTED 21
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w 23 Tutorial, Dynamic Analysis sha
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w 3 USER INTERFACE 3.1 INTRODUCTION
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w Simulation Paused 27 User Interfa
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w Keys on Main Window New model Ope
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w Rotate viewpoint left (decrement
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w General: StaticsMethod: Whole Sys
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w A text data file saved by OrcaFle
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w 37 User Interface, Model Browser
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w Cut/Copy Cut or Copy the selected
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w 3.4.1 Using Libraries 41 User Int
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w 43 User Interface, Libraries Once
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w 3.5.1 File Menu New Deletes all o
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w New Vessel New Line New 6D Buoy N
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w 3.5.5 View Menu Change Graphics M
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w Preferences 51 User Interface, Me
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w 53 User Interface, 3D Views 3D Vi
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w 55 User Interface, 3D Views � D
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w 57 User Interface, 3D Views a lin
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w 59 User Interface, 3D Views � F
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w Replay Period 61 User Interface,
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w Frame interval in real time 63 Us
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w Numeric 65 User Interface, Data F
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w � For lines you must specify th
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w 69 User Interface, Results this i
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w 71 User Interface, Results Let th
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w 73 User Interface, Results remain
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w Results 75 User Interface, Result
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w Replays 77 User Interface, Graphs
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w Axes 79 User Interface, Spreadshe
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w Command Line Parameters 81 User I
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w Wire Frame Graphics Codec 83 User
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Automation, Batch Processing Multi-
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Automation, Batch Processing 88 w N
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Automation, Batch Processing Assign
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Automation, Batch Processing Line T
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Automation, Batch Processing SHEAR7
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Automation, Batch Processing PolarT
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Automation, Batch Processing Figure
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Automation, Text Data Files Data in
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Automation, Text Data Files Selecte
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Automation, Text Data Files SHEAR7L
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Automation, Text Data Files 4.3.2 A
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Automation, Post-processing 108 w F
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Automation, Post-processing 110 w N
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Automation, Post-processing Referen
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Automation, Post-processing Command
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Automation, Post-processing Figure:
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w 5 THEORY 5.1 COORDINATE SYSTEMS 1
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w 125 Theory, Object Connections Di
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w 127 Theory, Static Analysis Final
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w 129 Theory, Static Analysis metho
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w 131 Theory, Dynamic Analysis for
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w Static Starting Position Simulati
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w 135 Theory, Friction Theory The n
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w where μ = magnitude of the vecto
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w 139 Theory, Extreme Value Statist
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w where σ = GPD scale parameter ξ
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w 143 Theory, Environment Theory Th
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w where Pu(z) = Nc(z/D)su(z)D Pu-su
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w 147 Theory, Environment Theory
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w Repenetration Offset After Uplift
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w 151 Theory, Environment Theory sp
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w Extrapolation Stretching 153 Theo
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w 155 Theory, Environment Theory st
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w 157 Theory, Vessel Theory individ
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w 159 Theory, Vessel Theory RAOs ca
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w 161 Theory, Vessel Theory Notes:
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w 163 Theory, Vessel Theory ω is t
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w surge/sway/heave M M.L roll/pitch
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w 167 Theory, Vessel Theory that co
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w 169 Theory, Vessel Theory separat
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w 171 Theory, Vessel Theory At this
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w Segment 1 Segment 2 Segment 3 Act
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w 175 Theory, Line Theory � If to
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w where component of M2 in the Sx2
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w The hysteresis model is described
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w � (90,90,90) sets Ex along -GX,
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w = v1 + p' + ω×p Therefore its a
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w y End A Stress ID z Stress OD O S
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w 5.12.16 Hydrodynamic and Aerodyna
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w 189 Theory, Line Theory Another w
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w Drag Chain Seabed Interaction 191
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w 193 Theory, Line Theory OrcaFlex
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w 195 Theory, 6D Buoy Theory clashi
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w 197 Theory, 6D Buoy Theory For Lu
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w 199 Theory, 6D Buoy Theory (due t
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w 201 Theory, 6D Buoy Theory Note:
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w α is the angle between the relat
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w 5.13.6 Contact Forces Contact For
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w Dynamic Analysis 207 Theory, Winc
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w 209 Theory, Shape Theory Finally,
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System Modelling: Data and Results,
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Page 432 and 433: Modal Analysis, Theory 432 w For si
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Fatigue Analysis, Load Cases Data f
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Fatigue Analysis, Load Cases Data f
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Fatigue Analysis, Analysis Data 442
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Fatigue Analysis, Integration Param
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Fatigue Analysis, Fatigue Points Ba
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Fatigue Analysis, How Damage is Cal
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VIV Toolbox, Frequency Domain Model
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